[HIVE-12640] Allow StatsOptimizer to optimize the query for Constant GroupBy keys

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.0.0
• Assignee: Hari Sankar Sivarama Subramaniyan
• Reporter: Hari Sankar Sivarama Subramaniyan
• Created: 09/Dec/15 22:13
• Updated: 16/Feb/16 23:53
• Resolved: 13/Jan/16 09:40

Description

hive> select count('1') from src group by '1';

In the above query, while performing StatsOptimizer optimization we can safely ignore the group by on the constant key '1' since the above query will return the same result as "select count('1') from src".

Exception:
If src is empty, according to the SQL standard,

 select count('1') from src group by '1'

and

 select count('1') from src

should produce 1 and 0 rows respectively.

Issue Links

• relates to: CALCITE-1016 "GROUP BY constant" on empty relation should return 0 rows
• links to: Reviewboard