Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/12222#discussion_r59635435
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/command/commands.scala
---
@@ -423,6 +424,100 @@ case class ShowTablePropertiesCommand(
}
/**
+ * A command for users to list the column names for a table. This function
creates a
+ * [[ShowColumnsCommand]] logical plan.
+ *
+ * The syntax of using this command in SQL is:
+ * {{{
+ * SHOW COLUMNS (FROM | IN) table_identifier [(FROM | IN) database];
+ * }}}
+ */
+case class ShowColumnsCommand(table: TableIdentifier) extends
RunnableCommand {
+ // The result of SHOW COLUMNS has one column called 'result'
+ override val output: Seq[Attribute] = {
+ AttributeReference("result", StringType, nullable = false)() :: Nil
+ }
+
+ override def run(sqlContext: SQLContext): Seq[Row] = {
+ val relation = sqlContext.sessionState.catalog.lookupRelation(table,
None)
+ relation.schema.fields.map { field =>
+ Row(field.name)
+ }
--- End diff --
It's better to get this information from the table metadata. 1 line:
```
sqlContext.sessionState.catalog.getTableMetadata(table).schema.map(_.name)
```
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