Github user xwu0226 commented on a diff in the pull request:
https://github.com/apache/spark/pull/16626#discussion_r97191587
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/command/tables.scala ---
@@ -168,6 +168,43 @@ case class AlterTableRenameCommand(
}
/**
+ * A command that add columns to a table
+ * The syntax of using this command in SQL is:
+ * {{{
+ * ALTER TABLE table_identifier
+ * ADD COLUMNS (col_name data_type [COMMENT col_comment], ...);
+ * }}}
+*/
+case class AlterTableAddColumnsCommand(
+ table: TableIdentifier,
+ columns: Seq[StructField]) extends RunnableCommand {
+ override def run(sparkSession: SparkSession): Seq[Row] = {
+ val catalog = sparkSession.sessionState.catalog
+ val catalogTable = DDLUtils.verifyAlterTableAddColumn(catalog, table)
+
+ // If an exception is thrown here we can just assume the table is
uncached;
+ // this can happen with Hive tables when the underlying catalog is
in-memory.
+ val wasCached =
Try(sparkSession.catalog.isCached(table.unquotedString)).getOrElse(false)
+ if (wasCached) {
+ try {
+ sparkSession.catalog.uncacheTable(table.unquotedString)
+ } catch {
+ case NonFatal(e) => log.warn(e.toString, e)
+ }
+ }
+ // Invalidate the table last, otherwise uncaching the table would load
the logical plan
+ // back into the hive metastore cache
+ catalog.refreshTable(table)
+
+ val newSchema = catalogTable.schema.copy(fields =
catalogTable.schema.fields ++ columns)
--- End diff --
We support partitioned tables. The test cases add include this case.
However, we don't support ALTER ADD COLUMNS to a particular partition, as
what Hive can do today. EX: `ALTER TABLE T1 PARTITION(c3=1) ADD COLUMNS .... `.
This is another potential feature to add if we maintain schema for a partition.
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