imback82 commented on a change in pull request #26182: [SPARK-29523][SQL] SHOW
COLUMNS should do multi-catalog resolution.
URL: https://github.com/apache/spark/pull/26182#discussion_r339350734
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/AstBuilder.scala
##########
@@ -2877,4 +2877,28 @@ class AstBuilder(conf: SQLConf) extends
SqlBaseBaseVisitor[AnyRef] with Logging
override def visitRefreshTable(ctx: RefreshTableContext): LogicalPlan =
withOrigin(ctx) {
RefreshTableStatement(visitMultipartIdentifier(ctx.multipartIdentifier()))
}
+
+ /**
+ * A command for users to list the column names for a table.
+ * This function creates a [[ShowColumnsStatement]] logical plan.
+ *
+ * The syntax of using this command in SQL is:
+ * {{{
+ * SHOW COLUMNS (FROM | IN) tableName=multipartIdentifier
+ * ((FROM | IN) namespace=multipartIdentifier)?
+ * }}}
+ */
+ override def visitShowColumns(ctx: ShowColumnsContext): LogicalPlan =
withOrigin(ctx) {
+ val table = visitMultipartIdentifier(ctx.tableName)
+ if (ctx.namespace != null) {
+ val namespace = visitMultipartIdentifier(ctx.namespace)
+ if (table.length > 1 && namespace.length > 1) {
+ throw new ParseException(
+ s"If namespace is defined, table can not be multipart:
${table.mkString(".")}", ctx)
+ }
+ ShowColumnsStatement(table, Some(namespace))
+ } else {
+ ShowColumnsStatement(table, None)
+ }
+ }
Review comment:
You can simplify the code a bit if you want:
```scala
val table = visitMultipartIdentifier(ctx.tableName)
val namespace =
Option(ctx.multipartIdentifier).map(visitMultipartIdentifier)
if (namespace.isDefined && namespace.get.length > 1 && table.length > 1)
{
throw new ParseException(
s"If namespace is defined, table can not be multipart:
${table.mkString(".")}", ctx)
}
ShowColumnsStatement(table, namespace)
```
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