Github user gatorsmile commented on a diff in the pull request:
https://github.com/apache/spark/pull/15717#discussion_r92120744
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/command/ddl.scala ---
@@ -274,6 +274,76 @@ case class AlterTableUnsetPropertiesCommand(
}
+
+/**
+ * A command to change the columns for a table, only support changing the
comments of non-partition
+ * columns for now.
+ *
+ * The syntax of using this command in SQL is:
+ * {{{
+ * ALTER TABLE table_identifier
+ * CHANGE [COLUMN] column_old_name column_new_name column_dataType
[COMMENT column_comment]
+ * [FIRST | AFTER column_name];
+ * }}}
+ */
+case class AlterTableChangeColumnsCommand(
+ tableName: TableIdentifier,
+ columns: Map[String, StructField]) extends RunnableCommand {
+
+ // TODO: support change column name/dataType/metadata/position.
+ override def run(sparkSession: SparkSession): Seq[Row] = {
+ val catalog = sparkSession.sessionState.catalog
+ val table = catalog.getTableMetadata(tableName)
+ val resolver = sparkSession.sessionState.conf.resolver
+ DDLUtils.verifyAlterTableType(catalog, table, isView = false)
+
+ // Create a map that converts the origin column to the new column with
changed comment, throw
+ // a Exception if the column reference is invalid or the column
name/dataType is changed.
+ val columnsMap = columns.map { case (oldName: String, newField:
StructField) =>
+ // Find the origin column from schema by column name.
+ val originColumn = findColumn(table.schema, oldName, resolver)
+ // Throw a Exception if the column name/dataType is changed.
+ if (!columnEqual(originColumn, newField, resolver)) {
+ throw new AnalysisException(
+ "ALTER TABLE CHANGE COLUMN is not supported for changing column
" +
+ s"'${originColumn.name}' with type '${originColumn.dataType}'
to " +
+ s"'${newField.name}' with type '${newField.dataType}'")
+ }
+ // Create a new column from the origin column with new comment.
--- End diff --
Actually, the rule is very simple.
> A countable noun always takes either the indefinite (a, an) or definite
(the) article when it is singular. When plural, it takes the definite article
if it refers to a definite, specific group and no article if it is used in a
general sense.
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