[GitHub] [flink] dawidwys commented on a change in pull request #10340: [FLINK-14978][table-api] Introduce constraint class hierarchy required for primary keys

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dawidwys commented on a change in pull request #10340: [FLINK-14978][table-api] Introduce constraint class hierarchy required for primary keys
URL: https://github.com/apache/flink/pull/10340#discussion_r352471857
 
 

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 File path: flink-table/flink-table-common/src/main/java/org/apache/flink/table/api/constraints/KeyConstraint.java
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 @@ -0,0 +1,100 @@
+/*
+ * 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.api.constraints;
+
+import org.apache.flink.annotation.PublicEvolving;
+import org.apache.flink.table.api.ValidationException;
+import org.apache.flink.table.expressions.FieldReferenceExpression;
+
+import java.util.List;
+import java.util.Objects;
+import java.util.stream.Collectors;
+
+import static org.apache.flink.util.Preconditions.checkNotNull;
+
+/**
+ * A unique key constraint. It can be declared also as a PRIMARY KEY.
+ *
+ * @see ConstraintType
+ */
+@PublicEvolving
+public final class KeyConstraint extends AbstractConstraint {
+	private final List<FieldReferenceExpression> columns;
 
 Review comment:
   Personally I would prefer to have the `FieldReferenceExpression` here. Exactly for the `inputIndex` and `fieldIndex info, as it might be helpful for a queries that have two inputs (it might not). In general I think schema should be fixed after every modification. In general `fieldIndex` should always be source of truth for any field references.
   
   Is it that hard though? The `KeyConstraint` class is sort of a second level API. Users should rather not use it. They should go against the `TableSchema` which exposes method `primaryKey(String name, String[] columns)`, which performs the resolution.
   
   This resolution has to be performed anyway at some point.

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