[HIVE-21152] Rewrite if expression to case and recognize simple case as an if

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.0.0-alpha-1
• Component/s: CBO
• Labels: pull-request-available
• Assignee: Zoltan Haindrich
• Reporter: Zoltan Haindrich
• Created: 23/Jan/19 08:22
• Updated: 17/Nov/22 08:55
• Resolved: 17/Feb/22 17:12

Description

• IF is not part of the sql standard; however given its special form its simpler - and currently in Hive it also has vectorized support
• people writing standard sql may write: CASE WHEN member=1 THEN attr+1 else attr+2 END which is essentially an if.

The idea is to rewrite IFs to CASEs for the cbo; and recognize simple "CASE"-s as IFs to get vectorization on them if possible

Issue Links

• links to: GitHub Pull Request #2791