Re: [PR] Introduce dynamic table append (druid)

[via GitHub]

kgyrtkirk commented on code in PR #15897:
URL: https://github.com/apache/druid/pull/15897#discussion_r1491016435


##########
sql/src/main/java/org/apache/druid/sql/calcite/planner/DruidSqlValidator.java:
##########
@@ -177,7 +177,7 @@ public void validateCall(SqlCall call, SqlValidatorScope 
scope)
     super.validateCall(call, scope);
   }
 
-  private CalciteContextException buildCalciteContextException(String message, 
SqlNode call)
+  public static CalciteContextException buildCalciteContextException(String 
message, SqlNode call)

Review Comment:
   better place?



##########
sql/src/main/java/org/apache/druid/sql/calcite/external/TableAppendMacro.java:
##########
@@ -0,0 +1,344 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.sql.calcite.external;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.calcite.plan.RelOptTable;
+import org.apache.calcite.rel.type.RelDataType;
+import org.apache.calcite.rel.type.RelDataTypeFactory;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.schema.TranslatableTable;
+import org.apache.calcite.sql.SqlCall;
+import org.apache.calcite.sql.SqlCallBinding;
+import org.apache.calcite.sql.SqlIdentifier;
+import org.apache.calcite.sql.SqlKind;
+import org.apache.calcite.sql.SqlNode;
+import org.apache.calcite.sql.SqlOperandCountRange;
+import org.apache.calcite.sql.SqlOperator;
+import org.apache.calcite.sql.SqlOperatorBinding;
+import org.apache.calcite.sql.parser.SqlParserPos;
+import org.apache.calcite.sql.type.ReturnTypes;
+import org.apache.calcite.sql.type.SqlOperandCountRanges;
+import org.apache.calcite.sql.type.SqlOperandMetadata;
+import org.apache.calcite.sql.type.SqlTypeFamily;
+import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.sql.validate.SqlUserDefinedTableMacro;
+import org.apache.calcite.sql.validate.SqlValidator;
+import org.apache.calcite.sql.validate.SqlValidatorCatalogReader;
+import org.apache.calcite.sql.validate.SqlValidatorTable;
+import org.apache.druid.java.util.common.StringUtils;
+import org.apache.druid.query.DataSource;
+import org.apache.druid.query.UnionDataSource;
+import org.apache.druid.segment.column.ColumnType;
+import org.apache.druid.segment.column.RowSignature;
+import org.apache.druid.segment.column.RowSignature.Builder;
+import org.apache.druid.server.security.Action;
+import org.apache.druid.server.security.Resource;
+import org.apache.druid.server.security.ResourceAction;
+import org.apache.druid.server.security.ResourceType;
+import org.apache.druid.sql.calcite.expression.AuthorizableOperator;
+import org.apache.druid.sql.calcite.expression.DruidExpression;
+import org.apache.druid.sql.calcite.expression.SqlOperatorConversion;
+import org.apache.druid.sql.calcite.planner.DruidSqlValidator;
+import org.apache.druid.sql.calcite.planner.PlannerContext;
+import org.apache.druid.sql.calcite.table.DatasourceMetadata;
+import org.apache.druid.sql.calcite.table.DatasourceTable;
+import org.apache.druid.sql.calcite.table.DatasourceTable.EffectiveMetadata;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+/**
+ * Dynamic table append.
+ *
+ * Enables to use: TABLE(APPEND('t1','t2')); which will provide a union view 
of the operand tables.
+ */
+public class TableAppendMacro extends SqlUserDefinedTableMacro implements 
AuthorizableOperator
+{
+
+  public static final OperatorConversion OPERATOR_CONVERSION = new 
OperatorConversion();
+  public static final SqlOperator APPEND_TABLE_MACRO = new TableAppendMacro();
+
+  private static class OperatorConversion implements SqlOperatorConversion
+  {
+    public static final String FUNCTION_NAME = "APPEND";
+
+    public OperatorConversion()
+    {
+    }
+
+    @Override
+    public SqlOperator calciteOperator()
+    {
+      return APPEND_TABLE_MACRO;
+    }
+
+    @Override
+    public DruidExpression toDruidExpression(PlannerContext plannerContext, 
RowSignature rowSignature, RexNode rexNode)
+    {
+      throw new IllegalStateException();
+    }
+  }
+
+  private TableAppendMacro()
+  {
+    super(
+        new SqlIdentifier(OperatorConversion.FUNCTION_NAME, SqlParserPos.ZERO),
+        SqlKind.OTHER_FUNCTION,
+        ReturnTypes.CURSOR,
+        null,
+        new OperandMetadata(),
+        null
+    );
+  }
+
+  private static class OperandMetadata implements SqlOperandMetadata
+  {
+    @Override
+    public boolean checkOperandTypes(SqlCallBinding callBinding, boolean 
throwOnFailure)
+    {
+      for (int i = 0; i < callBinding.getOperandCount(); i++) {
+        SqlNode operand = callBinding.operand(i);
+        if (!callBinding.isOperandLiteral(i, false)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not literal",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+
+        SqlTypeName typeName = callBinding.getOperandType(i).getSqlTypeName();
+        if (!SqlTypeFamily.CHARACTER.getTypeNames().contains(typeName)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not string",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+      }
+      return true;
+    }
+
+    @Override
+    public SqlOperandCountRange getOperandCountRange()
+    {
+      return SqlOperandCountRanges.from(1);
+    }
+
+    @Override
+    public String getAllowedSignatures(SqlOperator op, String opName)
+    {
+      return "APPEND( <TABLE_NAME>[, <TABLE_NAME> ...] )";
+    }
+
+    @Override
+    public List<RelDataType> paramTypes(RelDataTypeFactory typeFactory)
+    {
+      RelDataType t = typeFactory.createSqlType(SqlTypeName.VARCHAR);
+      return ImmutableList.<RelDataType>builder().add(t, t).build();
+    }
+
+    @Override
+    public List<String> paramNames()
+    {
+      return ImmutableList.<String>builder().add("tableName", 
"tableName").build();

Review Comment:
   
   
   changed it to `"tableName1", "tableName2"`
   



##########
sql/src/main/java/org/apache/druid/sql/calcite/external/TableAppendMacro.java:
##########
@@ -0,0 +1,309 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.sql.calcite.external;
+
+import org.apache.calcite.plan.RelOptTable;
+import org.apache.calcite.rel.type.RelDataType;
+import org.apache.calcite.rel.type.RelDataTypeFactory;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.schema.TranslatableTable;
+import org.apache.calcite.sql.SqlCall;
+import org.apache.calcite.sql.SqlCallBinding;
+import org.apache.calcite.sql.SqlIdentifier;
+import org.apache.calcite.sql.SqlKind;
+import org.apache.calcite.sql.SqlNode;
+import org.apache.calcite.sql.SqlOperandCountRange;
+import org.apache.calcite.sql.SqlOperator;
+import org.apache.calcite.sql.SqlOperatorBinding;
+import org.apache.calcite.sql.parser.SqlParserPos;
+import org.apache.calcite.sql.type.ReturnTypes;
+import org.apache.calcite.sql.type.SqlOperandCountRanges;
+import org.apache.calcite.sql.type.SqlOperandMetadata;
+import org.apache.calcite.sql.type.SqlTypeFamily;
+import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.sql.validate.SqlUserDefinedTableMacro;
+import org.apache.calcite.sql.validate.SqlValidator;
+import org.apache.calcite.sql.validate.SqlValidatorCatalogReader;
+import org.apache.calcite.sql.validate.SqlValidatorTable;
+import org.apache.curator.shaded.com.google.common.collect.ImmutableList;
+import org.apache.druid.error.InvalidInput;
+import org.apache.druid.java.util.common.StringUtils;
+import org.apache.druid.query.DataSource;
+import org.apache.druid.query.UnionDataSource;
+import org.apache.druid.segment.column.ColumnType;
+import org.apache.druid.segment.column.RowSignature;
+import org.apache.druid.segment.column.RowSignature.Builder;
+import org.apache.druid.server.security.Action;
+import org.apache.druid.server.security.Resource;
+import org.apache.druid.server.security.ResourceAction;
+import org.apache.druid.server.security.ResourceType;
+import org.apache.druid.sql.calcite.expression.AuthorizableOperator;
+import org.apache.druid.sql.calcite.expression.DruidExpression;
+import org.apache.druid.sql.calcite.expression.SqlOperatorConversion;
+import org.apache.druid.sql.calcite.planner.DruidSqlValidator;
+import org.apache.druid.sql.calcite.planner.PlannerContext;
+import org.apache.druid.sql.calcite.table.DatasourceMetadata;
+import org.apache.druid.sql.calcite.table.DatasourceTable;
+import org.apache.druid.sql.calcite.table.DatasourceTable.EffectiveMetadata;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+/**
+ * Dynamic table append.
+ *
+ * Enables to use: TABLE(APPEND('t1','t2')); which will provide a union view 
of the operand tables.
+ */
+public class TableAppendMacro extends SqlUserDefinedTableMacro implements 
AuthorizableOperator
+{
+
+  public static final OperatorConversion OPERATOR_CONVERSION = new 
OperatorConversion();
+  public static final SqlOperator APPEND_TABLE_MACRO = new TableAppendMacro();
+
+  private static class OperatorConversion implements SqlOperatorConversion
+  {
+    public static final String FUNCTION_NAME = "APPEND";
+
+    public OperatorConversion()
+    {
+    }
+
+    @Override
+    public SqlOperator calciteOperator()
+    {
+      return APPEND_TABLE_MACRO;
+    }
+
+    @Override
+    public DruidExpression toDruidExpression(PlannerContext plannerContext, 
RowSignature rowSignature, RexNode rexNode)
+    {
+      throw new IllegalStateException();
+    }
+  }
+
+  private TableAppendMacro()
+  {
+    super(
+        new SqlIdentifier(OperatorConversion.FUNCTION_NAME, SqlParserPos.ZERO),
+        SqlKind.OTHER_FUNCTION,
+        ReturnTypes.CURSOR,
+        null,
+        new OperandMetadata(),
+        null
+    );
+  }
+
+  private static class OperandMetadata implements SqlOperandMetadata
+  {
+    @Override
+    public boolean checkOperandTypes(SqlCallBinding callBinding, boolean 
throwOnFailure)
+    {
+      for (int i = 0; i < callBinding.getOperandCount(); i++) {
+        SqlNode operand = callBinding.operand(i);
+        if (!callBinding.isOperandLiteral(i, false)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not literal",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+
+        SqlTypeName typeName = callBinding.getOperandType(i).getSqlTypeName();
+        if (!SqlTypeFamily.CHARACTER.getTypeNames().contains(typeName)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not string",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+      }
+      return true;
+    }
+
+    @Override
+    public SqlOperandCountRange getOperandCountRange()
+    {
+      return SqlOperandCountRanges.from(2);
+    }
+
+    @Override
+    public String getAllowedSignatures(SqlOperator op, String opName)
+    {
+      return "APPEND( <TABLE_NAME>, <TABLE_NAME>[, <TABLE_NAME> ...] )";
+    }
+
+    @Override
+    public List<RelDataType> paramTypes(RelDataTypeFactory typeFactory)
+    {
+      RelDataType t = typeFactory.createSqlType(SqlTypeName.VARCHAR);
+      return ImmutableList.<RelDataType>builder().add(t, t).build();
+    }
+
+    @Override
+    public List<String> paramNames()
+    {
+      return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+    }
+  }
+
+  @Override
+  public List<String> getParamNames()
+  {
+    return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+  }
+
+  @Override
+  public TranslatableTable getTable(SqlOperatorBinding callBinding)
+  {
+    SqlValidator validator = ((SqlCallBinding) callBinding).getValidator();
+    List<RelOptTable> tables = getTables(callBinding, 
validator.getCatalogReader());
+    AppendDatasourceMetadata metadata = buildUnionDataSource(tables);
+    return new DatasourceTable(
+        metadata.values,
+        metadata,
+        EffectiveMetadata.of(metadata.values)
+    );
+  }
+
+  private List<RelOptTable> getTables(SqlOperatorBinding callBinding, 
SqlValidatorCatalogReader catalogReader)
+  {
+    List<RelOptTable> tables = new ArrayList<>();
+    for (int i = 0; i < callBinding.getOperandCount(); i++) {
+      if (!callBinding.isOperandLiteral(i, false)) {
+        throw new IllegalArgumentException(
+            "All arguments of call to macro "
+                + "APPEND should be literal. Actual argument #"
+                + i + " is not literal"
+        );

Review Comment:
   didn't notice this remained an `IllegalArgumentException` ; fixed it!



##########
sql/src/main/java/org/apache/druid/sql/calcite/external/TableAppendMacro.java:
##########
@@ -0,0 +1,309 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.sql.calcite.external;
+
+import org.apache.calcite.plan.RelOptTable;
+import org.apache.calcite.rel.type.RelDataType;
+import org.apache.calcite.rel.type.RelDataTypeFactory;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.schema.TranslatableTable;
+import org.apache.calcite.sql.SqlCall;
+import org.apache.calcite.sql.SqlCallBinding;
+import org.apache.calcite.sql.SqlIdentifier;
+import org.apache.calcite.sql.SqlKind;
+import org.apache.calcite.sql.SqlNode;
+import org.apache.calcite.sql.SqlOperandCountRange;
+import org.apache.calcite.sql.SqlOperator;
+import org.apache.calcite.sql.SqlOperatorBinding;
+import org.apache.calcite.sql.parser.SqlParserPos;
+import org.apache.calcite.sql.type.ReturnTypes;
+import org.apache.calcite.sql.type.SqlOperandCountRanges;
+import org.apache.calcite.sql.type.SqlOperandMetadata;
+import org.apache.calcite.sql.type.SqlTypeFamily;
+import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.sql.validate.SqlUserDefinedTableMacro;
+import org.apache.calcite.sql.validate.SqlValidator;
+import org.apache.calcite.sql.validate.SqlValidatorCatalogReader;
+import org.apache.calcite.sql.validate.SqlValidatorTable;
+import org.apache.curator.shaded.com.google.common.collect.ImmutableList;
+import org.apache.druid.error.InvalidInput;
+import org.apache.druid.java.util.common.StringUtils;
+import org.apache.druid.query.DataSource;
+import org.apache.druid.query.UnionDataSource;
+import org.apache.druid.segment.column.ColumnType;
+import org.apache.druid.segment.column.RowSignature;
+import org.apache.druid.segment.column.RowSignature.Builder;
+import org.apache.druid.server.security.Action;
+import org.apache.druid.server.security.Resource;
+import org.apache.druid.server.security.ResourceAction;
+import org.apache.druid.server.security.ResourceType;
+import org.apache.druid.sql.calcite.expression.AuthorizableOperator;
+import org.apache.druid.sql.calcite.expression.DruidExpression;
+import org.apache.druid.sql.calcite.expression.SqlOperatorConversion;
+import org.apache.druid.sql.calcite.planner.DruidSqlValidator;
+import org.apache.druid.sql.calcite.planner.PlannerContext;
+import org.apache.druid.sql.calcite.table.DatasourceMetadata;
+import org.apache.druid.sql.calcite.table.DatasourceTable;
+import org.apache.druid.sql.calcite.table.DatasourceTable.EffectiveMetadata;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+/**
+ * Dynamic table append.
+ *
+ * Enables to use: TABLE(APPEND('t1','t2')); which will provide a union view 
of the operand tables.
+ */
+public class TableAppendMacro extends SqlUserDefinedTableMacro implements 
AuthorizableOperator
+{
+
+  public static final OperatorConversion OPERATOR_CONVERSION = new 
OperatorConversion();
+  public static final SqlOperator APPEND_TABLE_MACRO = new TableAppendMacro();
+
+  private static class OperatorConversion implements SqlOperatorConversion
+  {
+    public static final String FUNCTION_NAME = "APPEND";
+
+    public OperatorConversion()
+    {
+    }
+
+    @Override
+    public SqlOperator calciteOperator()
+    {
+      return APPEND_TABLE_MACRO;
+    }
+
+    @Override
+    public DruidExpression toDruidExpression(PlannerContext plannerContext, 
RowSignature rowSignature, RexNode rexNode)
+    {
+      throw new IllegalStateException();
+    }
+  }
+
+  private TableAppendMacro()
+  {
+    super(
+        new SqlIdentifier(OperatorConversion.FUNCTION_NAME, SqlParserPos.ZERO),
+        SqlKind.OTHER_FUNCTION,
+        ReturnTypes.CURSOR,
+        null,
+        new OperandMetadata(),
+        null
+    );
+  }
+
+  private static class OperandMetadata implements SqlOperandMetadata
+  {
+    @Override
+    public boolean checkOperandTypes(SqlCallBinding callBinding, boolean 
throwOnFailure)
+    {
+      for (int i = 0; i < callBinding.getOperandCount(); i++) {
+        SqlNode operand = callBinding.operand(i);
+        if (!callBinding.isOperandLiteral(i, false)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not literal",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+
+        SqlTypeName typeName = callBinding.getOperandType(i).getSqlTypeName();
+        if (!SqlTypeFamily.CHARACTER.getTypeNames().contains(typeName)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not string",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+      }
+      return true;
+    }
+
+    @Override
+    public SqlOperandCountRange getOperandCountRange()
+    {
+      return SqlOperandCountRanges.from(2);
+    }
+
+    @Override
+    public String getAllowedSignatures(SqlOperator op, String opName)
+    {
+      return "APPEND( <TABLE_NAME>, <TABLE_NAME>[, <TABLE_NAME> ...] )";
+    }
+
+    @Override
+    public List<RelDataType> paramTypes(RelDataTypeFactory typeFactory)
+    {
+      RelDataType t = typeFactory.createSqlType(SqlTypeName.VARCHAR);
+      return ImmutableList.<RelDataType>builder().add(t, t).build();
+    }
+
+    @Override
+    public List<String> paramNames()
+    {
+      return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+    }
+  }
+
+  @Override
+  public List<String> getParamNames()
+  {
+    return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+  }
+
+  @Override
+  public TranslatableTable getTable(SqlOperatorBinding callBinding)
+  {
+    SqlValidator validator = ((SqlCallBinding) callBinding).getValidator();
+    List<RelOptTable> tables = getTables(callBinding, 
validator.getCatalogReader());
+    AppendDatasourceMetadata metadata = buildUnionDataSource(tables);
+    return new DatasourceTable(
+        metadata.values,
+        metadata,
+        EffectiveMetadata.of(metadata.values)
+    );
+  }
+
+  private List<RelOptTable> getTables(SqlOperatorBinding callBinding, 
SqlValidatorCatalogReader catalogReader)
+  {
+    List<RelOptTable> tables = new ArrayList<>();
+    for (int i = 0; i < callBinding.getOperandCount(); i++) {
+      if (!callBinding.isOperandLiteral(i, false)) {
+        throw new IllegalArgumentException(
+            "All arguments of call to macro "
+                + "APPEND should be literal. Actual argument #"
+                + i + " is not literal"
+        );
+      }
+      @Nullable
+      String tableName = callBinding.getOperandLiteralValue(i, String.class);
+      ImmutableList<String> tableNameList = 
ImmutableList.<String>builder().add(tableName).build();
+      SqlValidatorTable table = catalogReader.getTable(tableNameList);
+      if (table == null) {
+        throw DruidSqlValidator.buildCalciteContextException(
+            StringUtils.format("Table [%s] not found", tableName),
+            ((SqlCallBinding) callBinding).operand(i)
+        );
+      }
+      tables.add(table.unwrapOrThrow(RelOptTable.class));
+    }
+    return tables;
+  }
+
+  static class AppendDatasourceMetadata implements DatasourceMetadata
+  {
+    private final RowSignature values;
+    private final DataSource dataSource;
+
+    public AppendDatasourceMetadata(RowSignature values, List<DataSource> 
dataSources)
+    {
+      this.values = values;
+      this.dataSource = new UnionDataSource(dataSources);
+    }
+
+    @Override
+    public boolean isJoinable()
+    {
+      return false;
+    }
+
+    @Override
+    public boolean isBroadcast()
+    {
+      return false;
+    }
+
+    @Override
+    public DataSource dataSource()
+    {
+      return dataSource;
+    }
+  }
+
+  private AppendDatasourceMetadata buildUnionDataSource(List<RelOptTable> 
tables)
+  {
+    List<DataSource> dataSources = new ArrayList<>();
+    Map<String, ColumnType> fields = new LinkedHashMap<>();
+    Builder rowSignatureBuilder = RowSignature.builder();
+    for (RelOptTable relOptTable : tables) {
+      DatasourceTable table = relOptTable.unwrapOrThrow(DatasourceTable.class);
+      RowSignature rowSignature = table.getRowSignature();
+      for (String columnName : rowSignature.getColumnNames()) {
+        ColumnType currentType = rowSignature.getColumnType(columnName).get();
+        ColumnType existingType = fields.get(columnName);
+
+        if (existingType == null || existingType.equals(currentType)) {
+          fields.put(columnName, currentType);
+        } else {
+          try {
+            ColumnType commonType = 
ColumnType.leastRestrictiveType(currentType, existingType);
+            fields.put(columnName, commonType);
+          }
+          catch (Exception e) {
+            throw InvalidInput.exception(

Review Comment:
   It doesn't seem like `ColumnType.leastRestrictiveType` will throw exception 
right now - but that may change in the futue...better to handle it correctly
   
   changed it to use `buildCalciteContextException` 
   



##########
sql/src/main/java/org/apache/druid/sql/calcite/external/TableAppendMacro.java:
##########
@@ -0,0 +1,344 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.sql.calcite.external;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.calcite.plan.RelOptTable;
+import org.apache.calcite.rel.type.RelDataType;
+import org.apache.calcite.rel.type.RelDataTypeFactory;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.schema.TranslatableTable;
+import org.apache.calcite.sql.SqlCall;
+import org.apache.calcite.sql.SqlCallBinding;
+import org.apache.calcite.sql.SqlIdentifier;
+import org.apache.calcite.sql.SqlKind;
+import org.apache.calcite.sql.SqlNode;
+import org.apache.calcite.sql.SqlOperandCountRange;
+import org.apache.calcite.sql.SqlOperator;
+import org.apache.calcite.sql.SqlOperatorBinding;
+import org.apache.calcite.sql.parser.SqlParserPos;
+import org.apache.calcite.sql.type.ReturnTypes;
+import org.apache.calcite.sql.type.SqlOperandCountRanges;
+import org.apache.calcite.sql.type.SqlOperandMetadata;
+import org.apache.calcite.sql.type.SqlTypeFamily;
+import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.sql.validate.SqlUserDefinedTableMacro;
+import org.apache.calcite.sql.validate.SqlValidator;
+import org.apache.calcite.sql.validate.SqlValidatorCatalogReader;
+import org.apache.calcite.sql.validate.SqlValidatorTable;
+import org.apache.druid.java.util.common.StringUtils;
+import org.apache.druid.query.DataSource;
+import org.apache.druid.query.UnionDataSource;
+import org.apache.druid.segment.column.ColumnType;
+import org.apache.druid.segment.column.RowSignature;
+import org.apache.druid.segment.column.RowSignature.Builder;
+import org.apache.druid.server.security.Action;
+import org.apache.druid.server.security.Resource;
+import org.apache.druid.server.security.ResourceAction;
+import org.apache.druid.server.security.ResourceType;
+import org.apache.druid.sql.calcite.expression.AuthorizableOperator;
+import org.apache.druid.sql.calcite.expression.DruidExpression;
+import org.apache.druid.sql.calcite.expression.SqlOperatorConversion;
+import org.apache.druid.sql.calcite.planner.DruidSqlValidator;
+import org.apache.druid.sql.calcite.planner.PlannerContext;
+import org.apache.druid.sql.calcite.table.DatasourceMetadata;
+import org.apache.druid.sql.calcite.table.DatasourceTable;
+import org.apache.druid.sql.calcite.table.DatasourceTable.EffectiveMetadata;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+/**
+ * Dynamic table append.
+ *
+ * Enables to use: TABLE(APPEND('t1','t2')); which will provide a union view 
of the operand tables.
+ */
+public class TableAppendMacro extends SqlUserDefinedTableMacro implements 
AuthorizableOperator
+{
+
+  public static final OperatorConversion OPERATOR_CONVERSION = new 
OperatorConversion();
+  public static final SqlOperator APPEND_TABLE_MACRO = new TableAppendMacro();
+
+  private static class OperatorConversion implements SqlOperatorConversion
+  {
+    public static final String FUNCTION_NAME = "APPEND";
+
+    public OperatorConversion()
+    {
+    }
+
+    @Override
+    public SqlOperator calciteOperator()
+    {
+      return APPEND_TABLE_MACRO;
+    }
+
+    @Override
+    public DruidExpression toDruidExpression(PlannerContext plannerContext, 
RowSignature rowSignature, RexNode rexNode)
+    {
+      throw new IllegalStateException();
+    }
+  }
+
+  private TableAppendMacro()
+  {
+    super(
+        new SqlIdentifier(OperatorConversion.FUNCTION_NAME, SqlParserPos.ZERO),
+        SqlKind.OTHER_FUNCTION,
+        ReturnTypes.CURSOR,
+        null,
+        new OperandMetadata(),
+        null
+    );
+  }
+
+  private static class OperandMetadata implements SqlOperandMetadata

Review Comment:
   I had to do some back-and-forth before implementing these things; mostly 
because (as you've noticed) originally the tablemacro supposed to have a fixed 
number of arguments.
   
   I don't really understand why it needs to have fixed number of arguments...
   
   however I wanted to use [this 
logic](https://github.com/apache/calcite/blob/2558c13cdb8b6a8e1608112a902b1bf9d97b5386/core/src/main/java/org/apache/calcite/sql2rel/SqlToRelConverter.java#L2874)
 - but for that I had to retain the `SqlUserDefinedTableMacro` type; which 
wants `SqlOperandMetadata` which have the idea of fixed number of arguments....
   
   implementing `SqlOperandMetadata` made it work correctly - but `paramNames` 
and `paramTypes` remained odd...
   



##########
sql/src/main/java/org/apache/druid/sql/calcite/external/TableAppendMacro.java:
##########
@@ -0,0 +1,344 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.sql.calcite.external;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.calcite.plan.RelOptTable;
+import org.apache.calcite.rel.type.RelDataType;
+import org.apache.calcite.rel.type.RelDataTypeFactory;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.schema.TranslatableTable;
+import org.apache.calcite.sql.SqlCall;
+import org.apache.calcite.sql.SqlCallBinding;
+import org.apache.calcite.sql.SqlIdentifier;
+import org.apache.calcite.sql.SqlKind;
+import org.apache.calcite.sql.SqlNode;
+import org.apache.calcite.sql.SqlOperandCountRange;
+import org.apache.calcite.sql.SqlOperator;
+import org.apache.calcite.sql.SqlOperatorBinding;
+import org.apache.calcite.sql.parser.SqlParserPos;
+import org.apache.calcite.sql.type.ReturnTypes;
+import org.apache.calcite.sql.type.SqlOperandCountRanges;
+import org.apache.calcite.sql.type.SqlOperandMetadata;
+import org.apache.calcite.sql.type.SqlTypeFamily;
+import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.sql.validate.SqlUserDefinedTableMacro;
+import org.apache.calcite.sql.validate.SqlValidator;
+import org.apache.calcite.sql.validate.SqlValidatorCatalogReader;
+import org.apache.calcite.sql.validate.SqlValidatorTable;
+import org.apache.druid.java.util.common.StringUtils;
+import org.apache.druid.query.DataSource;
+import org.apache.druid.query.UnionDataSource;
+import org.apache.druid.segment.column.ColumnType;
+import org.apache.druid.segment.column.RowSignature;
+import org.apache.druid.segment.column.RowSignature.Builder;
+import org.apache.druid.server.security.Action;
+import org.apache.druid.server.security.Resource;
+import org.apache.druid.server.security.ResourceAction;
+import org.apache.druid.server.security.ResourceType;
+import org.apache.druid.sql.calcite.expression.AuthorizableOperator;
+import org.apache.druid.sql.calcite.expression.DruidExpression;
+import org.apache.druid.sql.calcite.expression.SqlOperatorConversion;
+import org.apache.druid.sql.calcite.planner.DruidSqlValidator;
+import org.apache.druid.sql.calcite.planner.PlannerContext;
+import org.apache.druid.sql.calcite.table.DatasourceMetadata;
+import org.apache.druid.sql.calcite.table.DatasourceTable;
+import org.apache.druid.sql.calcite.table.DatasourceTable.EffectiveMetadata;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+/**
+ * Dynamic table append.
+ *
+ * Enables to use: TABLE(APPEND('t1','t2')); which will provide a union view 
of the operand tables.
+ */
+public class TableAppendMacro extends SqlUserDefinedTableMacro implements 
AuthorizableOperator
+{
+
+  public static final OperatorConversion OPERATOR_CONVERSION = new 
OperatorConversion();
+  public static final SqlOperator APPEND_TABLE_MACRO = new TableAppendMacro();
+
+  private static class OperatorConversion implements SqlOperatorConversion
+  {
+    public static final String FUNCTION_NAME = "APPEND";
+
+    public OperatorConversion()
+    {
+    }
+
+    @Override
+    public SqlOperator calciteOperator()
+    {
+      return APPEND_TABLE_MACRO;
+    }
+
+    @Override
+    public DruidExpression toDruidExpression(PlannerContext plannerContext, 
RowSignature rowSignature, RexNode rexNode)
+    {
+      throw new IllegalStateException();
+    }
+  }
+
+  private TableAppendMacro()
+  {
+    super(
+        new SqlIdentifier(OperatorConversion.FUNCTION_NAME, SqlParserPos.ZERO),
+        SqlKind.OTHER_FUNCTION,
+        ReturnTypes.CURSOR,
+        null,
+        new OperandMetadata(),
+        null
+    );
+  }
+
+  private static class OperandMetadata implements SqlOperandMetadata
+  {
+    @Override
+    public boolean checkOperandTypes(SqlCallBinding callBinding, boolean 
throwOnFailure)
+    {
+      for (int i = 0; i < callBinding.getOperandCount(); i++) {
+        SqlNode operand = callBinding.operand(i);
+        if (!callBinding.isOperandLiteral(i, false)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not literal",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+
+        SqlTypeName typeName = callBinding.getOperandType(i).getSqlTypeName();
+        if (!SqlTypeFamily.CHARACTER.getTypeNames().contains(typeName)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not string",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+      }
+      return true;
+    }
+
+    @Override
+    public SqlOperandCountRange getOperandCountRange()
+    {
+      return SqlOperandCountRanges.from(1);
+    }
+
+    @Override
+    public String getAllowedSignatures(SqlOperator op, String opName)
+    {
+      return "APPEND( <TABLE_NAME>[, <TABLE_NAME> ...] )";
+    }
+
+    @Override
+    public List<RelDataType> paramTypes(RelDataTypeFactory typeFactory)
+    {
+      RelDataType t = typeFactory.createSqlType(SqlTypeName.VARCHAR);
+      return ImmutableList.<RelDataType>builder().add(t, t).build();
+    }
+
+    @Override
+    public List<String> paramNames()
+    {
+      return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+    }
+  }
+
+  @Override
+  public List<String> getParamNames()
+  {
+    return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+  }
+
+  @Override
+  public TranslatableTable getTable(SqlOperatorBinding operatorBinding)
+  {
+    SqlCallBinding callBinding = (SqlCallBinding) operatorBinding;
+    SqlValidator validator = callBinding.getValidator();
+
+    List<TableOperand> tables = getTables(callBinding, 
validator.getCatalogReader());
+    AppendDatasourceMetadata metadata = buildUnionDataSource(tables);
+    return new DatasourceTable(
+        metadata.values,
+        metadata,
+        EffectiveMetadata.of(metadata.values)
+    );
+  }
+
+  static class TableOperand
+  {
+    private final SqlNode sqlOperand;
+    private final SqlValidatorTable table;
+
+    public TableOperand(SqlNode sqlOperand, SqlValidatorTable table)
+    {
+      this.sqlOperand = sqlOperand;
+      this.table = table;
+    }
+
+    public RelOptTable getRelOptTable()
+    {
+      return table.unwrapOrThrow(RelOptTable.class);
+    }
+
+    public DatasourceTable getDataSourceTable()
+    {
+      return table.unwrapOrThrow(DatasourceTable.class);
+    }
+
+    public RowSignature getRowSignature()
+    {
+      return getDataSourceTable().getRowSignature();
+    }
+
+    public DataSource getDataSource()
+    {
+      return getDataSourceTable().getDataSource();
+    }
+  }
+
+  private List<TableOperand> getTables(SqlCallBinding callBinding, 
SqlValidatorCatalogReader catalogReader)
+  {
+    List<TableOperand> tables = new ArrayList<>();
+    for (int i = 0; i < callBinding.getOperandCount(); i++) {
+      if (!callBinding.isOperandLiteral(i, false)) {
+        throw DruidSqlValidator.buildCalciteContextException(
+            "All arguments of call to macro "
+                + "APPEND should be literal. Actual argument #"
+                + i + " is not literal",
+                callBinding.operand(i)
+        );
+      }
+      @Nullable

Review Comment:
   no; `null` is not a string literal either ; so it can't happen => but added 
a testcase ; in case that changes



##########
sql/src/main/java/org/apache/druid/sql/calcite/external/TableAppendMacro.java:
##########
@@ -0,0 +1,344 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.sql.calcite.external;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.calcite.plan.RelOptTable;
+import org.apache.calcite.rel.type.RelDataType;
+import org.apache.calcite.rel.type.RelDataTypeFactory;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.schema.TranslatableTable;
+import org.apache.calcite.sql.SqlCall;
+import org.apache.calcite.sql.SqlCallBinding;
+import org.apache.calcite.sql.SqlIdentifier;
+import org.apache.calcite.sql.SqlKind;
+import org.apache.calcite.sql.SqlNode;
+import org.apache.calcite.sql.SqlOperandCountRange;
+import org.apache.calcite.sql.SqlOperator;
+import org.apache.calcite.sql.SqlOperatorBinding;
+import org.apache.calcite.sql.parser.SqlParserPos;
+import org.apache.calcite.sql.type.ReturnTypes;
+import org.apache.calcite.sql.type.SqlOperandCountRanges;
+import org.apache.calcite.sql.type.SqlOperandMetadata;
+import org.apache.calcite.sql.type.SqlTypeFamily;
+import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.sql.validate.SqlUserDefinedTableMacro;
+import org.apache.calcite.sql.validate.SqlValidator;
+import org.apache.calcite.sql.validate.SqlValidatorCatalogReader;
+import org.apache.calcite.sql.validate.SqlValidatorTable;
+import org.apache.druid.java.util.common.StringUtils;
+import org.apache.druid.query.DataSource;
+import org.apache.druid.query.UnionDataSource;
+import org.apache.druid.segment.column.ColumnType;
+import org.apache.druid.segment.column.RowSignature;
+import org.apache.druid.segment.column.RowSignature.Builder;
+import org.apache.druid.server.security.Action;
+import org.apache.druid.server.security.Resource;
+import org.apache.druid.server.security.ResourceAction;
+import org.apache.druid.server.security.ResourceType;
+import org.apache.druid.sql.calcite.expression.AuthorizableOperator;
+import org.apache.druid.sql.calcite.expression.DruidExpression;
+import org.apache.druid.sql.calcite.expression.SqlOperatorConversion;
+import org.apache.druid.sql.calcite.planner.DruidSqlValidator;
+import org.apache.druid.sql.calcite.planner.PlannerContext;
+import org.apache.druid.sql.calcite.table.DatasourceMetadata;
+import org.apache.druid.sql.calcite.table.DatasourceTable;
+import org.apache.druid.sql.calcite.table.DatasourceTable.EffectiveMetadata;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+/**
+ * Dynamic table append.
+ *
+ * Enables to use: TABLE(APPEND('t1','t2')); which will provide a union view 
of the operand tables.
+ */
+public class TableAppendMacro extends SqlUserDefinedTableMacro implements 
AuthorizableOperator
+{
+
+  public static final OperatorConversion OPERATOR_CONVERSION = new 
OperatorConversion();
+  public static final SqlOperator APPEND_TABLE_MACRO = new TableAppendMacro();
+
+  private static class OperatorConversion implements SqlOperatorConversion
+  {
+    public static final String FUNCTION_NAME = "APPEND";
+
+    public OperatorConversion()
+    {
+    }
+
+    @Override
+    public SqlOperator calciteOperator()
+    {
+      return APPEND_TABLE_MACRO;
+    }
+
+    @Override
+    public DruidExpression toDruidExpression(PlannerContext plannerContext, 
RowSignature rowSignature, RexNode rexNode)
+    {
+      throw new IllegalStateException();
+    }
+  }
+
+  private TableAppendMacro()
+  {
+    super(
+        new SqlIdentifier(OperatorConversion.FUNCTION_NAME, SqlParserPos.ZERO),
+        SqlKind.OTHER_FUNCTION,
+        ReturnTypes.CURSOR,
+        null,
+        new OperandMetadata(),
+        null
+    );
+  }
+
+  private static class OperandMetadata implements SqlOperandMetadata
+  {
+    @Override
+    public boolean checkOperandTypes(SqlCallBinding callBinding, boolean 
throwOnFailure)
+    {
+      for (int i = 0; i < callBinding.getOperandCount(); i++) {
+        SqlNode operand = callBinding.operand(i);
+        if (!callBinding.isOperandLiteral(i, false)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not literal",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+
+        SqlTypeName typeName = callBinding.getOperandType(i).getSqlTypeName();
+        if (!SqlTypeFamily.CHARACTER.getTypeNames().contains(typeName)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not string",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+      }
+      return true;
+    }
+
+    @Override
+    public SqlOperandCountRange getOperandCountRange()
+    {
+      return SqlOperandCountRanges.from(1);
+    }
+
+    @Override
+    public String getAllowedSignatures(SqlOperator op, String opName)
+    {
+      return "APPEND( <TABLE_NAME>[, <TABLE_NAME> ...] )";
+    }
+
+    @Override
+    public List<RelDataType> paramTypes(RelDataTypeFactory typeFactory)
+    {
+      RelDataType t = typeFactory.createSqlType(SqlTypeName.VARCHAR);
+      return ImmutableList.<RelDataType>builder().add(t, t).build();
+    }
+
+    @Override
+    public List<String> paramNames()
+    {
+      return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+    }
+  }
+
+  @Override
+  public List<String> getParamNames()
+  {
+    return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+  }
+
+  @Override
+  public TranslatableTable getTable(SqlOperatorBinding operatorBinding)
+  {
+    SqlCallBinding callBinding = (SqlCallBinding) operatorBinding;
+    SqlValidator validator = callBinding.getValidator();
+
+    List<TableOperand> tables = getTables(callBinding, 
validator.getCatalogReader());
+    AppendDatasourceMetadata metadata = buildUnionDataSource(tables);
+    return new DatasourceTable(
+        metadata.values,
+        metadata,
+        EffectiveMetadata.of(metadata.values)
+    );
+  }
+
+  static class TableOperand
+  {
+    private final SqlNode sqlOperand;
+    private final SqlValidatorTable table;
+
+    public TableOperand(SqlNode sqlOperand, SqlValidatorTable table)
+    {
+      this.sqlOperand = sqlOperand;
+      this.table = table;
+    }
+
+    public RelOptTable getRelOptTable()
+    {
+      return table.unwrapOrThrow(RelOptTable.class);
+    }
+
+    public DatasourceTable getDataSourceTable()
+    {
+      return table.unwrapOrThrow(DatasourceTable.class);
+    }
+
+    public RowSignature getRowSignature()
+    {
+      return getDataSourceTable().getRowSignature();
+    }
+
+    public DataSource getDataSource()
+    {
+      return getDataSourceTable().getDataSource();
+    }
+  }
+
+  private List<TableOperand> getTables(SqlCallBinding callBinding, 
SqlValidatorCatalogReader catalogReader)
+  {
+    List<TableOperand> tables = new ArrayList<>();
+    for (int i = 0; i < callBinding.getOperandCount(); i++) {
+      if (!callBinding.isOperandLiteral(i, false)) {

Review Comment:
   right - this is not necessary; removed it!



##########
sql/src/test/java/org/apache/druid/sql/calcite/CalciteTableAppendTest.java:
##########
@@ -0,0 +1,214 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.sql.calcite;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.druid.error.DruidException;
+import org.apache.druid.sql.calcite.NotYetSupported.NotYetSupportedProcessor;
+import org.hamcrest.MatcherAssert;
+import org.junit.Assert;
+import org.junit.Rule;
+import org.junit.Test;
+
+public class CalciteTableAppendTest extends BaseCalciteQueryTest

Review Comment:
   added native queries



##########
sql/src/main/java/org/apache/druid/sql/calcite/table/DatasourceMetadata.java:
##########
@@ -0,0 +1,33 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.sql.calcite.table;
+
+import org.apache.druid.query.DataSource;
+
+public interface DatasourceMetadata
+{
+
+  DataSource dataSource();

Review Comment:
   apidoc?



##########
sql/src/main/java/org/apache/druid/sql/calcite/external/AppendTableMacro.java:
##########
@@ -0,0 +1,301 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.sql.calcite.external;
+
+import org.apache.calcite.plan.RelOptTable;
+import org.apache.calcite.rel.type.RelDataType;
+import org.apache.calcite.rel.type.RelDataTypeFactory;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.schema.TranslatableTable;
+import org.apache.calcite.sql.SqlCall;
+import org.apache.calcite.sql.SqlCallBinding;
+import org.apache.calcite.sql.SqlIdentifier;
+import org.apache.calcite.sql.SqlKind;
+import org.apache.calcite.sql.SqlNode;
+import org.apache.calcite.sql.SqlOperandCountRange;
+import org.apache.calcite.sql.SqlOperator;
+import org.apache.calcite.sql.SqlOperatorBinding;
+import org.apache.calcite.sql.parser.SqlParserPos;
+import org.apache.calcite.sql.type.ReturnTypes;
+import org.apache.calcite.sql.type.SqlOperandCountRanges;
+import org.apache.calcite.sql.type.SqlOperandMetadata;
+import org.apache.calcite.sql.type.SqlTypeFamily;
+import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.sql.validate.SqlUserDefinedTableMacro;
+import org.apache.calcite.sql.validate.SqlValidator;
+import org.apache.calcite.sql.validate.SqlValidatorCatalogReader;
+import org.apache.calcite.sql.validate.SqlValidatorTable;
+import org.apache.curator.shaded.com.google.common.collect.ImmutableList;
+import org.apache.druid.query.DataSource;
+import org.apache.druid.query.UnionDataSource;
+import org.apache.druid.segment.column.ColumnType;
+import org.apache.druid.segment.column.RowSignature;
+import org.apache.druid.segment.column.RowSignature.Builder;
+import org.apache.druid.server.security.Action;
+import org.apache.druid.server.security.Resource;
+import org.apache.druid.server.security.ResourceAction;
+import org.apache.druid.server.security.ResourceType;
+import org.apache.druid.sql.calcite.expression.AuthorizableOperator;
+import org.apache.druid.sql.calcite.expression.DruidExpression;
+import org.apache.druid.sql.calcite.expression.SqlOperatorConversion;
+import org.apache.druid.sql.calcite.planner.DruidSqlValidator;
+import org.apache.druid.sql.calcite.planner.PlannerContext;
+import org.apache.druid.sql.calcite.table.DatasourceMetadata;
+import org.apache.druid.sql.calcite.table.DatasourceTable;
+import org.apache.druid.sql.calcite.table.DatasourceTable.EffectiveMetadata;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+/**
+ * Dynamic table append.
+ *
+ * Enables to use: TABLE(APPEND('t1','t2')); which will provide a union view 
of the operand tables.
+ */
+public class AppendTableMacro extends SqlUserDefinedTableMacro implements 
AuthorizableOperator
+{
+
+  public static final OperatorConversion OPERATOR_CONVERSION = new 
OperatorConversion();
+  public static final SqlOperator APPEND_TABLE_MACRO = new AppendTableMacro();
+
+  private static class OperatorConversion implements SqlOperatorConversion
+  {
+    public static final String FUNCTION_NAME = "APPEND";
+
+    public OperatorConversion()
+    {
+    }
+
+    @Override
+    public SqlOperator calciteOperator()
+    {
+      return APPEND_TABLE_MACRO;
+    }
+
+    @Override
+    public DruidExpression toDruidExpression(PlannerContext plannerContext, 
RowSignature rowSignature, RexNode rexNode)
+    {
+      throw new IllegalStateException();
+    }
+  }
+
+  private AppendTableMacro()
+  {
+    super(
+        new SqlIdentifier(OperatorConversion.FUNCTION_NAME, SqlParserPos.ZERO),
+        SqlKind.OTHER_FUNCTION,
+        ReturnTypes.CURSOR,
+        null,
+        new OperandMetadata(),
+        null
+    );
+  }
+
+  private static class OperandMetadata implements SqlOperandMetadata
+  {
+    @Override
+    public boolean checkOperandTypes(SqlCallBinding callBinding, boolean 
throwOnFailure)
+    {
+      for (int i = 0; i < callBinding.getOperandCount(); i++) {
+        SqlNode operand = callBinding.operand(i);
+        if (!callBinding.isOperandLiteral(i, false)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not literal",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+        RelDataType type = callBinding.getOperandType(i);
+
+        SqlTypeName typeName = type.getSqlTypeName();
+
+        if (!SqlTypeFamily.CHARACTER.getTypeNames().contains(typeName)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not string",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+      }
+      return true;
+    }
+
+    @Override
+    public SqlOperandCountRange getOperandCountRange()
+    {
+      return SqlOperandCountRanges.from(2);
+    }
+
+    @Override
+    public String getAllowedSignatures(SqlOperator op, String opName)
+    {
+      return "APPEND( <TABLE_NAME>, <TABLE_NAME>[, <TABLE_NAME> ...] )";
+    }
+
+    @Override
+    public List<RelDataType> paramTypes(RelDataTypeFactory typeFactory)
+    {
+      RelDataType t = typeFactory.createSqlType(SqlTypeName.VARCHAR);
+      return ImmutableList.<RelDataType>builder().add(t, t).build();
+    }
+
+    @Override
+    public List<String> paramNames()
+    {
+      return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+    }
+  }
+
+  @Override
+  public List<String> getParamNames()
+  {
+    return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+  }
+
+  @Override
+  public TranslatableTable getTable(SqlOperatorBinding callBinding)
+  {
+    SqlCallBinding ss = (SqlCallBinding) callBinding;
+    SqlValidator validator = ss.getValidator();
+    SqlValidatorCatalogReader catalogReader = validator.getCatalogReader();
+    List<String> tableNames = getTableNames(callBinding);
+    List<RelOptTable> tables = getTables(catalogReader, tableNames);
+
+    AppendDatasourceMetadata metadata = buildUnionDataSource(tables);
+    return new DatasourceTable(
+        metadata.values,
+        metadata,
+        EffectiveMetadata.of(metadata.values)
+    );
+  }
+
+  static class AppendDatasourceMetadata implements DatasourceMetadata
+  {
+    private final RowSignature values;
+    private final DataSource dataSource;
+
+    public AppendDatasourceMetadata(RowSignature values, List<DataSource> 
dataSources)
+    {
+      this.values = values;
+      this.dataSource = new UnionDataSource(dataSources);
+    }
+
+    @Override
+    public boolean isJoinable()
+    {
+      return false;
+    }
+
+    @Override
+    public boolean isBroadcast()
+    {
+      return false;
+    }
+
+    @Override
+    public DataSource dataSource()
+    {
+      return dataSource;
+    }
+  }
+
+  private AppendDatasourceMetadata buildUnionDataSource(List<RelOptTable> 
tables)
+  {
+    List<DataSource> dataSources = new ArrayList<>();
+    Map<String, ColumnType> fields = new LinkedHashMap<>();
+    Builder rowSignatureBuilder = RowSignature.builder();
+    for (RelOptTable relOptTable : tables) {
+
+      DatasourceTable a = relOptTable.unwrapOrThrow(DatasourceTable.class);

Review Comment:
   rename



##########
sql/src/main/java/org/apache/druid/sql/calcite/external/TableAppendMacro.java:
##########
@@ -0,0 +1,344 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.sql.calcite.external;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.calcite.plan.RelOptTable;
+import org.apache.calcite.rel.type.RelDataType;
+import org.apache.calcite.rel.type.RelDataTypeFactory;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.schema.TranslatableTable;
+import org.apache.calcite.sql.SqlCall;
+import org.apache.calcite.sql.SqlCallBinding;
+import org.apache.calcite.sql.SqlIdentifier;
+import org.apache.calcite.sql.SqlKind;
+import org.apache.calcite.sql.SqlNode;
+import org.apache.calcite.sql.SqlOperandCountRange;
+import org.apache.calcite.sql.SqlOperator;
+import org.apache.calcite.sql.SqlOperatorBinding;
+import org.apache.calcite.sql.parser.SqlParserPos;
+import org.apache.calcite.sql.type.ReturnTypes;
+import org.apache.calcite.sql.type.SqlOperandCountRanges;
+import org.apache.calcite.sql.type.SqlOperandMetadata;
+import org.apache.calcite.sql.type.SqlTypeFamily;
+import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.sql.validate.SqlUserDefinedTableMacro;
+import org.apache.calcite.sql.validate.SqlValidator;
+import org.apache.calcite.sql.validate.SqlValidatorCatalogReader;
+import org.apache.calcite.sql.validate.SqlValidatorTable;
+import org.apache.druid.java.util.common.StringUtils;
+import org.apache.druid.query.DataSource;
+import org.apache.druid.query.UnionDataSource;
+import org.apache.druid.segment.column.ColumnType;
+import org.apache.druid.segment.column.RowSignature;
+import org.apache.druid.segment.column.RowSignature.Builder;
+import org.apache.druid.server.security.Action;
+import org.apache.druid.server.security.Resource;
+import org.apache.druid.server.security.ResourceAction;
+import org.apache.druid.server.security.ResourceType;
+import org.apache.druid.sql.calcite.expression.AuthorizableOperator;
+import org.apache.druid.sql.calcite.expression.DruidExpression;
+import org.apache.druid.sql.calcite.expression.SqlOperatorConversion;
+import org.apache.druid.sql.calcite.planner.DruidSqlValidator;
+import org.apache.druid.sql.calcite.planner.PlannerContext;
+import org.apache.druid.sql.calcite.table.DatasourceMetadata;
+import org.apache.druid.sql.calcite.table.DatasourceTable;
+import org.apache.druid.sql.calcite.table.DatasourceTable.EffectiveMetadata;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+/**
+ * Dynamic table append.
+ *
+ * Enables to use: TABLE(APPEND('t1','t2')); which will provide a union view 
of the operand tables.
+ */
+public class TableAppendMacro extends SqlUserDefinedTableMacro implements 
AuthorizableOperator
+{
+
+  public static final OperatorConversion OPERATOR_CONVERSION = new 
OperatorConversion();
+  public static final SqlOperator APPEND_TABLE_MACRO = new TableAppendMacro();
+
+  private static class OperatorConversion implements SqlOperatorConversion
+  {
+    public static final String FUNCTION_NAME = "APPEND";
+
+    public OperatorConversion()
+    {
+    }
+
+    @Override
+    public SqlOperator calciteOperator()
+    {
+      return APPEND_TABLE_MACRO;
+    }
+
+    @Override
+    public DruidExpression toDruidExpression(PlannerContext plannerContext, 
RowSignature rowSignature, RexNode rexNode)
+    {
+      throw new IllegalStateException();
+    }
+  }
+
+  private TableAppendMacro()
+  {
+    super(
+        new SqlIdentifier(OperatorConversion.FUNCTION_NAME, SqlParserPos.ZERO),
+        SqlKind.OTHER_FUNCTION,
+        ReturnTypes.CURSOR,
+        null,
+        new OperandMetadata(),
+        null
+    );
+  }
+
+  private static class OperandMetadata implements SqlOperandMetadata
+  {
+    @Override
+    public boolean checkOperandTypes(SqlCallBinding callBinding, boolean 
throwOnFailure)
+    {
+      for (int i = 0; i < callBinding.getOperandCount(); i++) {
+        SqlNode operand = callBinding.operand(i);
+        if (!callBinding.isOperandLiteral(i, false)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not literal",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+
+        SqlTypeName typeName = callBinding.getOperandType(i).getSqlTypeName();
+        if (!SqlTypeFamily.CHARACTER.getTypeNames().contains(typeName)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not string",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+      }
+      return true;
+    }
+
+    @Override
+    public SqlOperandCountRange getOperandCountRange()
+    {
+      return SqlOperandCountRanges.from(1);
+    }
+
+    @Override
+    public String getAllowedSignatures(SqlOperator op, String opName)
+    {
+      return "APPEND( <TABLE_NAME>[, <TABLE_NAME> ...] )";
+    }
+
+    @Override
+    public List<RelDataType> paramTypes(RelDataTypeFactory typeFactory)
+    {
+      RelDataType t = typeFactory.createSqlType(SqlTypeName.VARCHAR);
+      return ImmutableList.<RelDataType>builder().add(t, t).build();
+    }
+
+    @Override
+    public List<String> paramNames()
+    {
+      return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+    }
+  }
+
+  @Override
+  public List<String> getParamNames()
+  {
+    return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+  }
+
+  @Override
+  public TranslatableTable getTable(SqlOperatorBinding operatorBinding)
+  {
+    SqlCallBinding callBinding = (SqlCallBinding) operatorBinding;
+    SqlValidator validator = callBinding.getValidator();
+
+    List<TableOperand> tables = getTables(callBinding, 
validator.getCatalogReader());
+    AppendDatasourceMetadata metadata = buildUnionDataSource(tables);
+    return new DatasourceTable(
+        metadata.values,
+        metadata,
+        EffectiveMetadata.of(metadata.values)
+    );
+  }
+
+  static class TableOperand
+  {
+    private final SqlNode sqlOperand;
+    private final SqlValidatorTable table;
+
+    public TableOperand(SqlNode sqlOperand, SqlValidatorTable table)
+    {
+      this.sqlOperand = sqlOperand;
+      this.table = table;
+    }
+
+    public RelOptTable getRelOptTable()
+    {
+      return table.unwrapOrThrow(RelOptTable.class);
+    }
+
+    public DatasourceTable getDataSourceTable()
+    {
+      return table.unwrapOrThrow(DatasourceTable.class);
+    }
+
+    public RowSignature getRowSignature()
+    {
+      return getDataSourceTable().getRowSignature();
+    }
+
+    public DataSource getDataSource()
+    {
+      return getDataSourceTable().getDataSource();
+    }
+  }
+
+  private List<TableOperand> getTables(SqlCallBinding callBinding, 
SqlValidatorCatalogReader catalogReader)
+  {
+    List<TableOperand> tables = new ArrayList<>();
+    for (int i = 0; i < callBinding.getOperandCount(); i++) {
+      if (!callBinding.isOperandLiteral(i, false)) {
+        throw DruidSqlValidator.buildCalciteContextException(
+            "All arguments of call to macro "
+                + "APPEND should be literal. Actual argument #"
+                + i + " is not literal",
+                callBinding.operand(i)
+        );
+      }
+      @Nullable
+      String tableName = callBinding.getOperandLiteralValue(i, String.class);
+      ImmutableList<String> tableNameList = 
ImmutableList.<String>builder().add(tableName).build();
+      SqlValidatorTable table = catalogReader.getTable(tableNameList);
+      if (table == null) {
+        throw DruidSqlValidator.buildCalciteContextException(
+            StringUtils.format("Table [%s] not found", tableName),
+            callBinding.operand(i)
+        );
+      }
+      tables.add(new TableOperand(callBinding.operand(i), table));
+    }
+    return tables;
+  }
+
+  static class AppendDatasourceMetadata implements DatasourceMetadata
+  {
+    private final RowSignature values;
+    private final DataSource dataSource;
+
+    public AppendDatasourceMetadata(RowSignature values, List<DataSource> 
dataSources)
+    {
+      this.values = values;
+      this.dataSource = new UnionDataSource(dataSources);
+    }
+
+    @Override
+    public boolean isJoinable()
+    {
+      return false;
+    }
+
+    @Override
+    public boolean isBroadcast()
+    {
+      return false;
+    }
+
+    @Override
+    public DataSource dataSource()
+    {
+      return dataSource;
+    }
+  }
+
+  private AppendDatasourceMetadata buildUnionDataSource(List<TableOperand> 
tables)
+  {
+    List<DataSource> dataSources = new ArrayList<>();
+    Map<String, ColumnType> fields = new LinkedHashMap<>();
+    Builder rowSignatureBuilder = RowSignature.builder();
+    for (TableOperand table : tables) {
+      RowSignature rowSignature = table.getRowSignature();
+      for (String columnName : rowSignature.getColumnNames()) {
+        ColumnType currentType = rowSignature.getColumnType(columnName).get();
+        ColumnType existingType = fields.get(columnName);
+
+        if (existingType == null || existingType.equals(currentType)) {
+          fields.put(columnName, currentType);
+        } else {
+          try {
+            ColumnType commonType = 
ColumnType.leastRestrictiveType(currentType, existingType);
+            fields.put(columnName, commonType);
+          }
+          catch (Exception e) {

Review Comment:
   don't think anything else might be coming out; changed it



##########
sql/src/test/java/org/apache/druid/sql/calcite/CalciteTableAppendTest.java:
##########
@@ -0,0 +1,214 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.sql.calcite;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.druid.error.DruidException;
+import org.apache.druid.sql.calcite.NotYetSupported.NotYetSupportedProcessor;
+import org.hamcrest.MatcherAssert;
+import org.junit.Assert;
+import org.junit.Rule;
+import org.junit.Test;
+
+public class CalciteTableAppendTest extends BaseCalciteQueryTest
+{
+  @Rule(order = 0)
+  public NotYetSupportedProcessor negativeTestProcessor = new 
NotYetSupportedProcessor();
+
+  @Test
+  public void testUnion()
+  {
+    testBuilder()
+        .sql("select dim1,null as dim4 from foo union all select dim1,dim4 
from numfoo")
+        .expectedResults(
+            ImmutableList.of(
+                new Object[] {"", null},
+                new Object[] {"10.1", null},
+                new Object[] {"2", null},
+                new Object[] {"1", null},
+                new Object[] {"def", null},
+                new Object[] {"abc", null},
+                new Object[] {"", "a"},
+                new Object[] {"10.1", "a"},
+                new Object[] {"2", "a"},
+                new Object[] {"1", "b"},
+                new Object[] {"def", "b"},
+                new Object[] {"abc", "b"}
+            )
+        )
+        .run();
+  }
+
+  @Test
+  public void testAppend2()
+  {
+    testBuilder()
+        .sql("select dim1,dim4,d1,f1 from TABLE(APPEND('foo','numfoo')) u")
+        .expectedResults(
+            ResultMatchMode.RELAX_NULLS,
+            ImmutableList.of(
+                new Object[] {"", null, null, null},
+                new Object[] {"10.1", null, null, null},
+                new Object[] {"2", null, null, null},
+                new Object[] {"1", null, null, null},
+                new Object[] {"def", null, null, null},
+                new Object[] {"abc", null, null, null},
+                new Object[] {"", "a", 1.0D, 1.0F},
+                new Object[] {"10.1", "a", 1.7D, 0.1F},
+                new Object[] {"2", "a", 0.0D, 0.0F},
+                new Object[] {"1", "b", null, null},
+                new Object[] {"def", "b", null, null},
+                new Object[] {"abc", "b", null, null}
+            )
+        )
+        .expectedLogicalPlan(
+            ""
+                + "LogicalProject(exprs=[[$1, $8, $11, $13]])\n"
+                + "  LogicalTableScan(table=[[APPEND]])\n"
+        )
+        .run();
+  }
+
+  @Test
+  public void testAppendSameTableMultipleTimes()
+  {
+    testBuilder()
+        .sql("select dim1,dim4,d1,f1 from TABLE(APPEND('foo','numfoo','foo')) 
u where dim1='2'")
+        .expectedResults(
+            ResultMatchMode.RELAX_NULLS,
+            ImmutableList.of(
+                new Object[] {"2", null, null, null},
+                new Object[] {"2", null, null, null},
+                new Object[] {"2", "a", 0.0D, 0.0F}
+            )
+        )
+        .run();
+  }
+
+  @Test
+  public void testAppendtSingleTableIsValid()
+  {
+    testBuilder()
+        .sql("select dim1 from TABLE(APPEND('foo')) u")
+        .expectedResults(
+            ImmutableList.of(
+                new Object[] {""},
+                new Object[] {"10.1"},
+                new Object[] {"2"},
+                new Object[] {"1"},
+                new Object[] {"def"},
+                new Object[] {"abc"}
+            )
+        )
+        .run();
+  }
+
+  @Test
+  public void testAppendtNoTableIsInvalid()
+  {
+    try {
+      testBuilder()
+          .sql("select dim1 from TABLE(APPEND()) u")
+          .run();
+      Assert.fail("query execution should fail");
+    }
+    catch (DruidException e) {
+      MatcherAssert.assertThat(
+          e,
+          invalidSqlIs("No match found for function signature APPEND() (line 
[1], column [24])")
+      );
+    }
+  }
+
+  @Test
+  public void testAppendNoTableIsInvalid()
+  {
+    try {
+      testBuilder()
+          .sql("select dim1 from TABLE(APPEND()) u")
+          .run();
+      Assert.fail("query execution should fail");
+    }
+    catch (DruidException e) {
+      MatcherAssert.assertThat(
+          e,
+          invalidSqlIs("No match found for function signature APPEND() (line 
[1], column [24])")
+      );
+    }
+  }
+
+  @Test
+  public void testAppendtSingleTableIsInvalidArg()
+  {
+    try {
+      testBuilder()
+          .sql("select dim1 from TABLE(APPEND('foo',111)) u")
+          .run();
+      Assert.fail("query execution should fail");
+    }
+    catch (DruidException e) {
+      MatcherAssert.assertThat(
+          e,
+          invalidSqlIs(
+              "All arguments to APPEND should be literal strings. Argument #1 
is not string (line [1], column [37])"

Review Comment:
   totally agree - changed it!



##########
sql/src/main/java/org/apache/druid/sql/calcite/external/TableAppendMacro.java:
##########
@@ -0,0 +1,344 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.sql.calcite.external;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.calcite.plan.RelOptTable;
+import org.apache.calcite.rel.type.RelDataType;
+import org.apache.calcite.rel.type.RelDataTypeFactory;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.schema.TranslatableTable;
+import org.apache.calcite.sql.SqlCall;
+import org.apache.calcite.sql.SqlCallBinding;
+import org.apache.calcite.sql.SqlIdentifier;
+import org.apache.calcite.sql.SqlKind;
+import org.apache.calcite.sql.SqlNode;
+import org.apache.calcite.sql.SqlOperandCountRange;
+import org.apache.calcite.sql.SqlOperator;
+import org.apache.calcite.sql.SqlOperatorBinding;
+import org.apache.calcite.sql.parser.SqlParserPos;
+import org.apache.calcite.sql.type.ReturnTypes;
+import org.apache.calcite.sql.type.SqlOperandCountRanges;
+import org.apache.calcite.sql.type.SqlOperandMetadata;
+import org.apache.calcite.sql.type.SqlTypeFamily;
+import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.sql.validate.SqlUserDefinedTableMacro;
+import org.apache.calcite.sql.validate.SqlValidator;
+import org.apache.calcite.sql.validate.SqlValidatorCatalogReader;
+import org.apache.calcite.sql.validate.SqlValidatorTable;
+import org.apache.druid.java.util.common.StringUtils;
+import org.apache.druid.query.DataSource;
+import org.apache.druid.query.UnionDataSource;
+import org.apache.druid.segment.column.ColumnType;
+import org.apache.druid.segment.column.RowSignature;
+import org.apache.druid.segment.column.RowSignature.Builder;
+import org.apache.druid.server.security.Action;
+import org.apache.druid.server.security.Resource;
+import org.apache.druid.server.security.ResourceAction;
+import org.apache.druid.server.security.ResourceType;
+import org.apache.druid.sql.calcite.expression.AuthorizableOperator;
+import org.apache.druid.sql.calcite.expression.DruidExpression;
+import org.apache.druid.sql.calcite.expression.SqlOperatorConversion;
+import org.apache.druid.sql.calcite.planner.DruidSqlValidator;
+import org.apache.druid.sql.calcite.planner.PlannerContext;
+import org.apache.druid.sql.calcite.table.DatasourceMetadata;
+import org.apache.druid.sql.calcite.table.DatasourceTable;
+import org.apache.druid.sql.calcite.table.DatasourceTable.EffectiveMetadata;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+/**
+ * Dynamic table append.
+ *
+ * Enables to use: TABLE(APPEND('t1','t2')); which will provide a union view 
of the operand tables.
+ */
+public class TableAppendMacro extends SqlUserDefinedTableMacro implements 
AuthorizableOperator
+{
+
+  public static final OperatorConversion OPERATOR_CONVERSION = new 
OperatorConversion();
+  public static final SqlOperator APPEND_TABLE_MACRO = new TableAppendMacro();
+
+  private static class OperatorConversion implements SqlOperatorConversion
+  {
+    public static final String FUNCTION_NAME = "APPEND";
+
+    public OperatorConversion()
+    {
+    }
+
+    @Override
+    public SqlOperator calciteOperator()
+    {
+      return APPEND_TABLE_MACRO;
+    }
+
+    @Override
+    public DruidExpression toDruidExpression(PlannerContext plannerContext, 
RowSignature rowSignature, RexNode rexNode)
+    {
+      throw new IllegalStateException();
+    }
+  }
+
+  private TableAppendMacro()
+  {
+    super(
+        new SqlIdentifier(OperatorConversion.FUNCTION_NAME, SqlParserPos.ZERO),
+        SqlKind.OTHER_FUNCTION,
+        ReturnTypes.CURSOR,
+        null,
+        new OperandMetadata(),
+        null
+    );
+  }
+
+  private static class OperandMetadata implements SqlOperandMetadata
+  {
+    @Override
+    public boolean checkOperandTypes(SqlCallBinding callBinding, boolean 
throwOnFailure)
+    {
+      for (int i = 0; i < callBinding.getOperandCount(); i++) {
+        SqlNode operand = callBinding.operand(i);
+        if (!callBinding.isOperandLiteral(i, false)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not literal",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+
+        SqlTypeName typeName = callBinding.getOperandType(i).getSqlTypeName();
+        if (!SqlTypeFamily.CHARACTER.getTypeNames().contains(typeName)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not string",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+      }
+      return true;
+    }
+
+    @Override
+    public SqlOperandCountRange getOperandCountRange()
+    {
+      return SqlOperandCountRanges.from(1);
+    }
+
+    @Override
+    public String getAllowedSignatures(SqlOperator op, String opName)
+    {
+      return "APPEND( <TABLE_NAME>[, <TABLE_NAME> ...] )";
+    }
+
+    @Override
+    public List<RelDataType> paramTypes(RelDataTypeFactory typeFactory)
+    {
+      RelDataType t = typeFactory.createSqlType(SqlTypeName.VARCHAR);
+      return ImmutableList.<RelDataType>builder().add(t, t).build();
+    }
+
+    @Override
+    public List<String> paramNames()
+    {
+      return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+    }
+  }
+
+  @Override
+  public List<String> getParamNames()
+  {
+    return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+  }
+
+  @Override
+  public TranslatableTable getTable(SqlOperatorBinding operatorBinding)
+  {
+    SqlCallBinding callBinding = (SqlCallBinding) operatorBinding;
+    SqlValidator validator = callBinding.getValidator();
+
+    List<TableOperand> tables = getTables(callBinding, 
validator.getCatalogReader());
+    AppendDatasourceMetadata metadata = buildUnionDataSource(tables);
+    return new DatasourceTable(
+        metadata.values,
+        metadata,
+        EffectiveMetadata.of(metadata.values)
+    );
+  }
+
+  static class TableOperand
+  {
+    private final SqlNode sqlOperand;
+    private final SqlValidatorTable table;
+
+    public TableOperand(SqlNode sqlOperand, SqlValidatorTable table)
+    {
+      this.sqlOperand = sqlOperand;
+      this.table = table;
+    }
+
+    public RelOptTable getRelOptTable()
+    {
+      return table.unwrapOrThrow(RelOptTable.class);
+    }
+
+    public DatasourceTable getDataSourceTable()
+    {
+      return table.unwrapOrThrow(DatasourceTable.class);
+    }
+
+    public RowSignature getRowSignature()
+    {
+      return getDataSourceTable().getRowSignature();
+    }
+
+    public DataSource getDataSource()
+    {
+      return getDataSourceTable().getDataSource();
+    }
+  }
+
+  private List<TableOperand> getTables(SqlCallBinding callBinding, 
SqlValidatorCatalogReader catalogReader)
+  {
+    List<TableOperand> tables = new ArrayList<>();
+    for (int i = 0; i < callBinding.getOperandCount(); i++) {
+      if (!callBinding.isOperandLiteral(i, false)) {
+        throw DruidSqlValidator.buildCalciteContextException(
+            "All arguments of call to macro "
+                + "APPEND should be literal. Actual argument #"
+                + i + " is not literal",
+                callBinding.operand(i)
+        );
+      }
+      @Nullable
+      String tableName = callBinding.getOperandLiteralValue(i, String.class);
+      ImmutableList<String> tableNameList = 
ImmutableList.<String>builder().add(tableName).build();
+      SqlValidatorTable table = catalogReader.getTable(tableNameList);

Review Comment:
   no - or not yet; `ProcedureNamespace` is deriving the type for the 
arguments; so can't use plain identifiers => 
   
   with string arguments I was not able to make it work
   
   I don't know if its possible to do that right now - but it would be nice to 
have that; most likely the direct identifier approach will be the best.
   Anyway - if its a CTE; then there will be real subquery inputs; which 
wouldn't be easy to handle right now....or I just don't see a way to make that 
work



##########
sql/src/main/java/org/apache/druid/sql/calcite/external/TableAppendMacro.java:
##########
@@ -0,0 +1,344 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.sql.calcite.external;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.calcite.plan.RelOptTable;
+import org.apache.calcite.rel.type.RelDataType;
+import org.apache.calcite.rel.type.RelDataTypeFactory;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.schema.TranslatableTable;
+import org.apache.calcite.sql.SqlCall;
+import org.apache.calcite.sql.SqlCallBinding;
+import org.apache.calcite.sql.SqlIdentifier;
+import org.apache.calcite.sql.SqlKind;
+import org.apache.calcite.sql.SqlNode;
+import org.apache.calcite.sql.SqlOperandCountRange;
+import org.apache.calcite.sql.SqlOperator;
+import org.apache.calcite.sql.SqlOperatorBinding;
+import org.apache.calcite.sql.parser.SqlParserPos;
+import org.apache.calcite.sql.type.ReturnTypes;
+import org.apache.calcite.sql.type.SqlOperandCountRanges;
+import org.apache.calcite.sql.type.SqlOperandMetadata;
+import org.apache.calcite.sql.type.SqlTypeFamily;
+import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.sql.validate.SqlUserDefinedTableMacro;
+import org.apache.calcite.sql.validate.SqlValidator;
+import org.apache.calcite.sql.validate.SqlValidatorCatalogReader;
+import org.apache.calcite.sql.validate.SqlValidatorTable;
+import org.apache.druid.java.util.common.StringUtils;
+import org.apache.druid.query.DataSource;
+import org.apache.druid.query.UnionDataSource;
+import org.apache.druid.segment.column.ColumnType;
+import org.apache.druid.segment.column.RowSignature;
+import org.apache.druid.segment.column.RowSignature.Builder;
+import org.apache.druid.server.security.Action;
+import org.apache.druid.server.security.Resource;
+import org.apache.druid.server.security.ResourceAction;
+import org.apache.druid.server.security.ResourceType;
+import org.apache.druid.sql.calcite.expression.AuthorizableOperator;
+import org.apache.druid.sql.calcite.expression.DruidExpression;
+import org.apache.druid.sql.calcite.expression.SqlOperatorConversion;
+import org.apache.druid.sql.calcite.planner.DruidSqlValidator;
+import org.apache.druid.sql.calcite.planner.PlannerContext;
+import org.apache.druid.sql.calcite.table.DatasourceMetadata;
+import org.apache.druid.sql.calcite.table.DatasourceTable;
+import org.apache.druid.sql.calcite.table.DatasourceTable.EffectiveMetadata;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+/**
+ * Dynamic table append.
+ *
+ * Enables to use: TABLE(APPEND('t1','t2')); which will provide a union view 
of the operand tables.
+ */
+public class TableAppendMacro extends SqlUserDefinedTableMacro implements 
AuthorizableOperator
+{
+
+  public static final OperatorConversion OPERATOR_CONVERSION = new 
OperatorConversion();
+  public static final SqlOperator APPEND_TABLE_MACRO = new TableAppendMacro();
+
+  private static class OperatorConversion implements SqlOperatorConversion
+  {
+    public static final String FUNCTION_NAME = "APPEND";
+
+    public OperatorConversion()
+    {
+    }
+
+    @Override
+    public SqlOperator calciteOperator()
+    {
+      return APPEND_TABLE_MACRO;
+    }
+
+    @Override
+    public DruidExpression toDruidExpression(PlannerContext plannerContext, 
RowSignature rowSignature, RexNode rexNode)
+    {
+      throw new IllegalStateException();
+    }
+  }
+
+  private TableAppendMacro()
+  {
+    super(
+        new SqlIdentifier(OperatorConversion.FUNCTION_NAME, SqlParserPos.ZERO),
+        SqlKind.OTHER_FUNCTION,
+        ReturnTypes.CURSOR,
+        null,
+        new OperandMetadata(),
+        null
+    );
+  }
+
+  private static class OperandMetadata implements SqlOperandMetadata
+  {
+    @Override
+    public boolean checkOperandTypes(SqlCallBinding callBinding, boolean 
throwOnFailure)
+    {
+      for (int i = 0; i < callBinding.getOperandCount(); i++) {
+        SqlNode operand = callBinding.operand(i);
+        if (!callBinding.isOperandLiteral(i, false)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not literal",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+
+        SqlTypeName typeName = callBinding.getOperandType(i).getSqlTypeName();
+        if (!SqlTypeFamily.CHARACTER.getTypeNames().contains(typeName)) {
+          if (throwOnFailure) {
+            throw DruidSqlValidator.buildCalciteContextException(
+                "All arguments to APPEND should be literal strings. "
+                    + "Argument #" + i + " is not string",
+                operand
+            );
+          } else {
+            return false;
+          }
+        }
+      }
+      return true;
+    }
+
+    @Override
+    public SqlOperandCountRange getOperandCountRange()
+    {
+      return SqlOperandCountRanges.from(1);
+    }
+
+    @Override
+    public String getAllowedSignatures(SqlOperator op, String opName)
+    {
+      return "APPEND( <TABLE_NAME>[, <TABLE_NAME> ...] )";
+    }
+
+    @Override
+    public List<RelDataType> paramTypes(RelDataTypeFactory typeFactory)
+    {
+      RelDataType t = typeFactory.createSqlType(SqlTypeName.VARCHAR);
+      return ImmutableList.<RelDataType>builder().add(t, t).build();
+    }
+
+    @Override
+    public List<String> paramNames()
+    {
+      return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+    }
+  }
+
+  @Override
+  public List<String> getParamNames()
+  {
+    return ImmutableList.<String>builder().add("tableName", 
"tableName").build();
+  }
+
+  @Override
+  public TranslatableTable getTable(SqlOperatorBinding operatorBinding)
+  {
+    SqlCallBinding callBinding = (SqlCallBinding) operatorBinding;
+    SqlValidator validator = callBinding.getValidator();
+
+    List<TableOperand> tables = getTables(callBinding, 
validator.getCatalogReader());
+    AppendDatasourceMetadata metadata = buildUnionDataSource(tables);
+    return new DatasourceTable(
+        metadata.values,
+        metadata,
+        EffectiveMetadata.of(metadata.values)
+    );
+  }
+
+  static class TableOperand
+  {
+    private final SqlNode sqlOperand;
+    private final SqlValidatorTable table;
+
+    public TableOperand(SqlNode sqlOperand, SqlValidatorTable table)
+    {
+      this.sqlOperand = sqlOperand;
+      this.table = table;
+    }
+
+    public RelOptTable getRelOptTable()
+    {
+      return table.unwrapOrThrow(RelOptTable.class);
+    }
+
+    public DatasourceTable getDataSourceTable()
+    {
+      return table.unwrapOrThrow(DatasourceTable.class);
+    }
+
+    public RowSignature getRowSignature()
+    {
+      return getDataSourceTable().getRowSignature();
+    }
+
+    public DataSource getDataSource()
+    {
+      return getDataSourceTable().getDataSource();
+    }
+  }
+
+  private List<TableOperand> getTables(SqlCallBinding callBinding, 
SqlValidatorCatalogReader catalogReader)
+  {
+    List<TableOperand> tables = new ArrayList<>();
+    for (int i = 0; i < callBinding.getOperandCount(); i++) {
+      if (!callBinding.isOperandLiteral(i, false)) {
+        throw DruidSqlValidator.buildCalciteContextException(
+            "All arguments of call to macro "
+                + "APPEND should be literal. Actual argument #"
+                + i + " is not literal",
+                callBinding.operand(i)
+        );
+      }
+      @Nullable
+      String tableName = callBinding.getOperandLiteralValue(i, String.class);
+      ImmutableList<String> tableNameList = 
ImmutableList.<String>builder().add(tableName).build();
+      SqlValidatorTable table = catalogReader.getTable(tableNameList);
+      if (table == null) {
+        throw DruidSqlValidator.buildCalciteContextException(
+            StringUtils.format("Table [%s] not found", tableName),
+            callBinding.operand(i)
+        );
+      }
+      tables.add(new TableOperand(callBinding.operand(i), table));
+    }
+    return tables;
+  }
+
+  static class AppendDatasourceMetadata implements DatasourceMetadata
+  {
+    private final RowSignature values;
+    private final DataSource dataSource;
+
+    public AppendDatasourceMetadata(RowSignature values, List<DataSource> 
dataSources)
+    {
+      this.values = values;
+      this.dataSource = new UnionDataSource(dataSources);
+    }
+
+    @Override
+    public boolean isJoinable()
+    {
+      return false;
+    }
+
+    @Override
+    public boolean isBroadcast()
+    {
+      return false;
+    }
+
+    @Override
+    public DataSource dataSource()
+    {
+      return dataSource;
+    }
+  }
+
+  private AppendDatasourceMetadata buildUnionDataSource(List<TableOperand> 
tables)
+  {
+    List<DataSource> dataSources = new ArrayList<>();
+    Map<String, ColumnType> fields = new LinkedHashMap<>();
+    Builder rowSignatureBuilder = RowSignature.builder();

Review Comment:
   oh - right! I've extracted it into a method as well!



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