[SPARK-21335] support un-aliased subquery

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.3.0
• Fix Version/s: 2.3.0
• Component/s: SQL
• Labels: release-notes
• Assignee: Wenchen Fan
• Reporter: Wenchen Fan
• Created: 07/Jul/17 04:02
• Updated: 27/Jun/18 03:41
• Resolved: 07/Jul/17 12:05

Description

un-aliased subquery is supported by Spark SQL for a long time. Its semantic was not well defined and has confusing behaviors, and it's not a standard SQL syntax, so we disallowed it in https://issues.apache.org/jira/browse/SPARK-20690 .

However, this is a breaking change, and we do have existing queries using un-aliased subquery. We should add the support back and fix its semantic.

After the fix, there is no syntax change from branch 2.2 to master, but we invalid a weird use case:
SELECT v.i from (SELECT i FROM v). Now this query will throw analysis exception because users should not be able to use the qualifier inside a subquery.

Issue Links

• supercedes: SPARK-20690 Subqueries in FROM should have alias names
• links to: [Github] Pull Request #18559 (cloud-fan)
• links to: [Github] Pull Request #21647 (cnZach)