dawidwys commented on code in PR #23612:
URL: https://github.com/apache/flink/pull/23612#discussion_r1448743070


##########
flink-table/flink-table-planner/src/main/java/org/apache/flink/table/planner/operations/converters/SqlShowDatabasesConverter.java:
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@@ -0,0 +1,51 @@
+/*
+ * 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.flink.table.planner.operations.converters;
+
+import org.apache.flink.sql.parser.dql.SqlShowDatabases;
+import org.apache.flink.table.catalog.CatalogManager;
+import org.apache.flink.table.operations.Operation;
+import org.apache.flink.table.operations.ShowDatabasesOperation;
+
+/** A converter for {@link SqlShowDatabases}. */
+public class SqlShowDatabasesConverter implements 
SqlNodeConverter<SqlShowDatabases> {
+
+    @Override
+    public Operation convertSqlNode(SqlShowDatabases sqlShowDatabases, 
ConvertContext context) {
+        if (sqlShowDatabases.getPreposition() == null) {
+            return new ShowDatabasesOperation(
+                    sqlShowDatabases.getLikeType(),
+                    sqlShowDatabases.getLikeSqlPattern(),
+                    sqlShowDatabases.isNotLike());
+        } else {
+            CatalogManager catalogManager = context.getCatalogManager();
+            String[] fullCatalogName = sqlShowDatabases.getCatalog();
+            String catalogName =
+                    fullCatalogName.length == 0
+                            ? catalogManager.getCurrentCatalog()
+                            : fullCatalogName[0];

Review Comment:
   I am referring to the `SqlShowDatabasesConverter#convertSqlNode`:
   ```
           if (sqlShowDatabases.getPreposition() == null) {
   ...
           } else {
               String[] fullCatalogName = sqlShowDatabases.getCatalog();
               String catalogName =
                       fullCatalogName.length == 0
   ```
   
   Is it possible that you have a preposition, but the catalog name is not 
present: `fullCatalogName.length == 0`. What is the equivalent SQL query that 
results in such a situation?



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