[GitHub] [flink] dawidwys commented on a change in pull request #10213: [FLINK-12846][table-common] Carry primary key information in TableSchema

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dawidwys 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_r346829178
 
 

 ##########
 File path: flink-table/flink-table-common/src/main/java/org/apache/flink/table/api/TableSchema.java
 ##########
 @@ -22,32 +22,57 @@
 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 and
+ * constraint information (e.g. primary key, unique key).
+ *
+ * <p>Concepts about primary key and unique key:</p>
+ * <ul>
+ *     <li>
+ *         Primary key and unique key can consist of single or multiple columns (fields).
+ *     </li>
+ *     <li>
+ *         A primary key or unique key on source will be simply trusted, we won't validate the
+ *         constraint. The primary key and unique key information will then be used for query
+ *         optimization. If a bounded or unbounded table source defines any primary key or
+ *         unique 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 or unique key on sink is a weak constraint. Currently, we won't validate
+ *         the constraint, but we may add some check in the future to validate whether the
+ *         primary/unique key of the query matches the primary/unique key of the sink during
+ *         compile time.
+ *     </li>
+ *     <li>
+ *         The difference between primary key and unique key is that there can be only one primary
+ *         key and there can be more than one unique key. And a primary key doesn't need to be
+ *         declared in unique key list again.
 
 Review comment:
   ```suggestion
    *         declared in the unique key list again.
   ```

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