[HIVE-5709] Extend Join merging logic to merge 2 Joins when one Join expression list is a subset of the other.

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: Query Processor
• Assignee: Unassigned
• Reporter: Harish Butani
• Created: 31/Oct/13 17:27
• Updated: 31/Oct/13 17:59

Description

As pointed out by ashutoshc here: https://reviews.apache.org/r/14953/

For the following query

select p1.name, p2.name, p3.name
from part p1 join p2 on p1.name = p2.name and p1.key = p2.key join 
part p3 on p1.name = p3.name

2 jobs are generated:

• p1 join p2 on name, key
• join p3 on name

This can be done as:

• 1 3-way join of p1,p2,p3 on name
• followed by a Filter on p1.key = p2.key

This is valid only for inner joins.
This can be done by extending the Merge Join logic to check for a subset relation between 2 QBJoinTree expression lists.