[CALCITE-3355] Deduce whether CASE and COALESCE may produce NULL values

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.20.0
• Fix Version/s: 1.22.0
• Component/s: core
• Labels: pull-request-available
• Assignee: Chunwei Lei
• Reporter: Kirill Kozlov
• Created: 17/Sep/19 22:25
• Updated: 21/Mar/20 11:49
• Resolved: 04/Dec/19 02:34

Description

When executing queries like: 
"SELECT COALESCE(name, 'unknown') as name_out FROM PCOLLECTION"
(input 'name' is nullable)

There is a need to know whether the result is nullable or not (in this case - not). During validation stage "COALESCE" is being transformed (via SqlValidatorImpl.performUnconditionalRewrites) into a "CASE" statement, which currently does not determine nullability of a result.

Issue Links

• Blocked: BEAM-7610 SELECT COALESCE(...) isn't inferred as non-nullable field
• fixes: CALCITE-3850 AssertionError when converts a SQL parse tree into a relational algebra expression
• links to: GitHub Pull Request #1611