[GitHub] [flink] lsyldliu commented on a diff in pull request #19193: [FLINK-26813[SQL-API] Supports ADD/MODIFY column/watermark/constraint syntax parse for ALTER TABLE

[GitBox <gi...@apache.org>]

lsyldliu commented on code in PR #19193:
URL: https://github.com/apache/flink/pull/19193#discussion_r911668145


##########
flink-table/flink-sql-parser/src/main/java/org/apache/flink/sql/parser/ddl/position/SqlTableColumnPosition.java:
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@@ -0,0 +1,104 @@
+/*
+ *  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.sql.parser.ddl.position;
+
+import org.apache.flink.sql.parser.ddl.SqlTableColumn;
+
+import org.apache.calcite.sql.SqlCall;
+import org.apache.calcite.sql.SqlIdentifier;
+import org.apache.calcite.sql.SqlKind;
+import org.apache.calcite.sql.SqlLiteral;
+import org.apache.calcite.sql.SqlNode;
+import org.apache.calcite.sql.SqlOperator;
+import org.apache.calcite.sql.SqlSpecialOperator;
+import org.apache.calcite.sql.SqlWriter;
+import org.apache.calcite.sql.parser.SqlParserPos;
+import org.apache.calcite.util.ImmutableNullableList;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+import java.util.List;
+
+/** SqlNode to describe table column and its position. */
+public class SqlTableColumnPosition extends SqlCall {
+
+    private static final SqlOperator OPERATOR =
+            new SqlSpecialOperator("SqlTableColumnPosition", SqlKind.OTHER);
+
+    private final SqlTableColumn column;
+    private final SqlLiteral positionSpec;
+    @Nullable private final SqlIdentifier referencedColumn;
+
+    public SqlTableColumnPosition(
+            SqlParserPos pos,
+            SqlTableColumn column,
+            SqlLiteral positionSpec,
+            @Nullable SqlIdentifier referencedColumn) {
+        super(pos);
+        this.column = column;
+        this.positionSpec = positionSpec;
+        this.referencedColumn = referencedColumn;
+    }
+
+    public boolean isFirstColumn() {
+        return positionSpec.getValueAs(SqlColumnPosSpec.class) == SqlColumnPosSpec.FIRST;
+    }
+
+    public boolean isAfterReferencedColumn() {
+        return positionSpec.getValueAs(SqlColumnPosSpec.class) == SqlColumnPosSpec.AFTER
+                && referencedColumn != null;
+    }
+
+    public SqlTableColumn getColumn() {
+        return column;
+    }
+
+    public SqlLiteral getPositionSpec() {
+        return positionSpec;
+    }
+
+    @Nullable
+    public SqlIdentifier getAfterReferencedColumn() {
+        return referencedColumn;
+    }
+
+    @Nonnull
+    @Override
+    public SqlOperator getOperator() {
+        return OPERATOR;
+    }
+
+    @Nonnull
+    @Override
+    public List<SqlNode> getOperandList() {
+        return ImmutableNullableList.of(column, positionSpec, referencedColumn);
+    }
+
+    @Override
+    public void unparse(SqlWriter writer, int leftPrec, int rightPrec) {
+        column.unparse(writer, leftPrec, rightPrec);
+        if (isFirstColumn()) {
+            positionSpec.unparse(writer, leftPrec, rightPrec);
+        } else if (isAfterReferencedColumn()) {
+            positionSpec.unparse(writer, leftPrec, rightPrec);
+            referencedColumn.unparse(writer, leftPrec, rightPrec);
+        }

Review Comment:
   Here can't throw exception, it is default behavior. I've add comment here.



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