fsk119 commented on code in PR #21577:
URL: https://github.com/apache/flink/pull/21577#discussion_r1060254282
##########
flink-table/flink-table-common/src/main/java/org/apache/flink/table/catalog/TableChange.java:
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@@ -276,6 +409,359 @@ public String toString() {
}
}
+ //
--------------------------------------------------------------------------------------------
+ // Modify Change
+ //
--------------------------------------------------------------------------------------------
+
+ /**
+ * A base schema change to modify a column. The modification includes:
+ *
+ * <ul>
+ * <li>change column data type
+ * <li>reorder column position
+ * <li>modify column comment
+ * <li>change the computed expression
+ * </ul>
+ *
+ * <p>Some fine-grained column changes are defined in the {@link
ModifyPhysicalColumnType},
+ * {@link ModifyColumnComment}, {@link ModifyColumnPosition} and {@link
ModifyColumnName}.
+ *
+ * <p>It is equal to the following statement:
+ *
+ * <pre>
+ * ALTER TABLE <table_name> MODIFY <column_definition>
COMMENT '<column_comment>' <column_position>
+ * </pre>
+ */
+ @PublicEvolving
+ class ModifyColumn implements TableChange {
+
+ protected final Column oldColumn;
+ protected final Column newColumn;
+
+ protected final @Nullable ColumnPosition newPosition;
+
+ public ModifyColumn(
+ Column oldColumn, Column newColumn, @Nullable ColumnPosition
newPosition) {
+ this.oldColumn = oldColumn;
+ this.newColumn = newColumn;
+ this.newPosition = newPosition;
+ }
+
+ /** Returns the original {@link Column} instance. */
+ public Column getOldColumn() {
+ return oldColumn;
+ }
+
+ /** Returns the modified {@link Column} instance. */
+ public Column getNewColumn() {
+ return newColumn;
+ }
+
+ /**
+ * Returns the position of the modified {@link Column} instance. When
the return value is
+ * null, it means modify the column at the original position. When the
return value is
+ * FIRST, it means move the modified column to the first. When the
return value is AFTER, it
+ * means move the column after the referred column.
+ */
+ public @Nullable ColumnPosition getNewPosition() {
+ return newPosition;
+ }
+
+ @Override
+ public boolean equals(Object o) {
+ if (this == o) {
+ return true;
+ }
+ if (!(o instanceof ModifyColumn)) {
+ return false;
+ }
+ ModifyColumn that = (ModifyColumn) o;
+ return Objects.equals(oldColumn, that.oldColumn)
+ && Objects.equals(newColumn, that.newColumn)
+ && Objects.equals(newPosition, that.newPosition);
+ }
+
+ @Override
+ public int hashCode() {
+ return Objects.hash(oldColumn, newColumn, newPosition);
+ }
+
+ @Override
+ public String toString() {
+ return "ModifyColumn{"
+ + "oldColumn="
+ + oldColumn
+ + ", newColumn="
+ + newColumn
+ + ", newPosition="
+ + newPosition
+ + '}';
+ }
+ }
+
+ /**
+ * A table change to modify the column comment.
+ *
+ * <p>It is equal to the following statement:
+ *
+ * <pre>
+ * ALTER TABLE <table_name> MODIFY <column_name>
<original_column_type> COMMENT '<new_column_comment>'
+ * </pre>
+ */
+ @PublicEvolving
+ class ModifyColumnComment extends ModifyColumn {
+
+ private final String newComment;
+
+ private ModifyColumnComment(Column oldColumn, String newComment) {
+ super(oldColumn, oldColumn.withComment(newComment), null);
+ this.newComment = newComment;
+ }
+
+ /** Get the new comment for the column. */
+ public String getNewComment() {
+ return newComment;
+ }
+
+ @Override
+ public boolean equals(Object o) {
+ return (o instanceof ModifyColumnComment) && super.equals(o);
+ }
+
+ @Override
+ public String toString() {
+ return "ModifyColumnComment{"
+ + "Column="
+ + oldColumn
+ + ", newComment='"
+ + newComment
+ + '\''
+ + '}';
+ }
+ }
+
+ /**
+ * A table change to modify the column position.
+ *
+ * <p>It is equal to the following statement:
+ *
+ * <pre>
+ * ALTER TABLE <table_name> MODIFY <column_name>
<original_column_type> <column_position>
+ * </pre>
+ */
+ @PublicEvolving
+ class ModifyColumnPosition extends ModifyColumn {
+
+ public ModifyColumnPosition(Column oldColumn, ColumnPosition
newPosition) {
+ super(oldColumn, oldColumn, newPosition);
+ }
+
+ @Override
+ public boolean equals(Object o) {
+ return (o instanceof ModifyColumnPosition) && super.equals(o);
+ }
+
+ @Override
+ public String toString() {
+ return "ModifyColumnPosition{"
+ + "Column="
+ + oldColumn
+ + ", newPosition="
+ + newPosition
+ + '}';
+ }
+ }
+
+ /**
+ * A table change that modify the physical column data type.
Review Comment:
No. If users want to support modifying the metadata column type, we should
introduce another class named `ModifyMetadataColumn`, which may also involve
the change of the metadata key.
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