sjwiesman commented on a change in pull request #10213:
[FLINK-12846][table-common] Carry primary key information in TableSchema
URL: https://github.com/apache/flink/pull/10213#discussion_r347416772
##########
File path:
flink-table/flink-table-common/src/main/java/org/apache/flink/table/api/TableSchema.java
##########
@@ -22,32 +22,49 @@
import org.apache.flink.api.common.typeinfo.TypeInformation;
import org.apache.flink.api.common.typeutils.CompositeType;
import org.apache.flink.table.types.DataType;
-import org.apache.flink.table.types.FieldsDataType;
-import org.apache.flink.table.types.logical.LogicalType;
import org.apache.flink.table.types.utils.TypeConversions;
import org.apache.flink.types.Row;
import org.apache.flink.util.Preconditions;
import java.util.ArrayList;
import java.util.Arrays;
-import java.util.Collections;
-import java.util.HashMap;
import java.util.List;
-import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
+import static java.util.Collections.emptyList;
import static org.apache.flink.table.api.DataTypes.FIELD;
import static org.apache.flink.table.api.DataTypes.Field;
import static org.apache.flink.table.api.DataTypes.ROW;
-import static
org.apache.flink.table.types.logical.LogicalTypeRoot.TIMESTAMP_WITHOUT_TIME_ZONE;
import static
org.apache.flink.table.types.utils.TypeConversions.fromDataTypeToLegacyInfo;
import static
org.apache.flink.table.types.utils.TypeConversions.fromLegacyInfoToDataType;
+import static
org.apache.flink.table.utils.TableSchemaValidation.validateNameTypeNumberEqual;
+import static
org.apache.flink.table.utils.TableSchemaValidation.validateSchema;
/**
- * A table schema that represents a table's structure with field names and
data types.
+ * A table schema that represents a table's structure with field names, data
types, watermark
+ * information and constraint information (e.g. primary key).
+ *
+ * <p>Concepts about primary key:</p>
+ * <ul>
+ * <li>
+ * Primary key can be consist of single or multiple columns (fields).
+ * </li>
+ * <li>
+ * A primary key on source will be simply trusted, we won't validate
the constraint.
+ * The primary key information will then be used for query
optimization. If a bounded
+ * or unbounded table source defines any primary key, it must contain
a unique value
+ * for each row of data. You cannot have two records having the same
value of that field(s).
+ * Otherwise, the result of query might be wrong.
+ * </li>
+ * <li>
+ * A primary key on sink is a weak constraint. Currently, we won't
validate the constraint,
Review comment:
```suggestion
* A primary key on sink is a weak constraint and is not validated
by Flink. However,
```
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