Gunther Hagleitner created HIVE-6189:
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Summary: Support top level union all statements
Key: HIVE-6189
URL: https://issues.apache.org/jira/browse/HIVE-6189
Project: Hive
Issue Type: Bug
Reporter: Gunther Hagleitner
Assignee: Gunther Hagleitner
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" recursion into the
select statements. However, it's not hard to do that in code.
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