[HIVE-6189] Support top level union all statements

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.13.0
• Assignee: Gunther Hagleitner
• Reporter: Gunther Hagleitner
• Created: 13/Jan/14 08:01
• Updated: 03/Mar/16 11:54
• Resolved: 15/Jan/14 23:53

Description

I've always wondered why union all has to be in subqueries in hive.

After looking at it, problems are:

• Hive Parser:
• Union happens at the wrong place (insert ... select ... union all select ...) is parsed as (insert select) union select.
• There are many rewrite rules in the parser to force any query into the a from - insert -select form. No doubt for historical reasons.
• Plan generation/semantic analysis assumes top level "TOK_QUERY" and not top level "TOK_UNION".

The rewrite rules don't work when we move the "UNION ALL" into the select statements. However, it's not hard to do that in code.

Issue Links

• relates to: HIVE-9002 union all does not generate correct result for order by and limit
• supercedes: HIVE-1398 Support union all without an outer select *
• links to: Review board