[HIVE-21537] Scalar query rewrite could be improved to not generate an extra join if subquery is guaranteed to produce atmost one row

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 4.0.0
• Fix Version/s: 4.0.0-alpha-1
• Component/s: Query Planning
• Labels: sub-query
• Assignee: Vineet Garg
• Reporter: Vineet Garg
• Created: 28/Mar/19 22:36
• Updated: 27/Feb/24 22:23
• Resolved: 01/Apr/19 23:16

Description

Currently Hive planner introduces this branch and later executes a rule to remove this branch if it could.
Subquery remove rule itself could check if subquery will produce max one row (using relmetadat's getMaxRowCount) and avoid introducing this branch.