[CALCITE-5294] Prune the null-generating side of an outer join if it is empty

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.33.0
• Component/s: core
• Labels: pull-request-available
• Assignee: Krisztian Kasa
• Reporter: Krisztian Kasa
• Created: 21/Sep/22 11:06
• Updated: 07/Feb/23 22:33
• Resolved: 24/Sep/22 05:16

Description

If a Join generates null on the right and the right branch of the join known never produces any rows the join can be replaced with the left branch and a project on top of it which contains the expressions come from the left branch and null constants from the right branch. Example:

select * from emp e
left outer join (select * from dept where false) as d on e.deptno = d.deptno

select 
  e.*, 
  cast(null as <dept_col0_type>) as <dept_col0_name>
  ... 
  cast(null as <dept_coln_type>) as <dept_coln_name> 
from emp

Issue Links

• relates to: CALCITE-5282 JdbcValues should add CAST on NULL values
• links to: GitHub Pull Request #2916