[SPARK-11705] Eliminate unnecessary Cartesian Join

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Cannot Reproduce
• Component/s: SQL
• Assignee: Unassigned
• Reporter: Zhan Zhang
• Created: 12/Nov/15 18:24
• Updated: 02/Dec/16 19:09
• Resolved: 02/Dec/16 19:09

Description

When we have some queries similar to following (don’t remember the exact form):
select * from a, b, c, d where a.key1 = c.key1 and b.key2 = c.key2 and c.key3 = d.key3

There will be a cartesian join between a and b. But if we just simply change the table order, for example from a, c, b, d, such cartesian join are eliminated.
Without such manual tuning, the query will never finish if a, b are big. But we should not relies on such manual optimization.