[HIVE-5258] Optimize aggregations without Group By followed by a Cross Join

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Assignee: Yin Huai
• Reporter: Yin Huai
• Created: 10/Sep/13 15:33
• Updated: 10/Sep/13 15:42

Description

For example, we should use a single MR job to execute the following query

SELECT *
FROM (SELECT tmp1.cnt1, tmp2.cnt2
      FROM (SELECT count(*) as cnt1
            FROM src1 x) tmp1
      JOIN (SELECT count(*) as cnt2
            FROM src1 y) tmp2) tmp3;

The reduce phase should have the reduce side GroupByOperators of tmp1 and tmp2, and the JoinOperator for the cross join.