[CALCITE-3845] CASE WHEN expression with nullability CAST is considered as reduced wrongly in ReduceExpressionsRule

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.23.0
• Component/s: core
• Labels: pull-request-available
• Assignee: Chunwei Lei
• Reporter: Chunwei Lei
• Created: 06/Mar/20 07:28
• Updated: 24/May/20 12:00
• Resolved: 10/Mar/20 10:24

Description

After ReduceExpressionsRule#reduceExpressionsInternal()[1],

CAST(CASE WHEN x then true WHEN y then TRUE ELSE false): boolean nullable (exp1) 

will be changed to 

WHEN x then CAST(true): boolean nullable WHEN y then CAST(true): boolean nullable ELSE CAST(false): boolean nullable.  (exp2)

Then exp1 is considered as reduced. In the next step, by ReduceExpressionsRule#simplifyPreservingType()[2], exp2 will be changed to 

CAST(CASE WHEN x then true WHEN y then TRUE ELSE false): boolean nullable (exp3)

, which is exactly the same as exp1.

Though exp1 is actually not reduced, it is still considered as reduced[3], which leads to CannotPlanException because of  setImportance(project, 0.0)[4].

 

[1]https://github.com/apache/calcite/blob/master/core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java#L618

[2]https://github.com/apache/calcite/blob/master/core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java#L624

 [3]https://github.com/apache/calcite/blob/master/core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java#L303

 [4]https://github.com/apache/calcite/blob/master/core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java#L312

 

Issue Links

• links to: GitHub Pull Request #1848