Chunwei Lei created CALCITE-3845:
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Summary: CASE WHEN expression with nullability CAST is considered
as reduced wrongly in ReduceExpressionsRule
Key: CALCITE-3845
URL: https://issues.apache.org/jira/browse/CALCITE-3845
Project: Calcite
Issue Type: Bug
Components: core
Reporter: Chunwei Lei
Assignee: Chunwei Lei
After ReduceExpressionsRule#reduceExpressionsInternal()[1],
{code:java}
CAST(CASE WHEN x then true WHEN y then TRUE ELSE false): boolean nullable
(exp1)
{code}
will be changed to
{code:java}
WHEN x then CAST(true): boolean nullable WHEN y then CAST(true): boolean
nullable ELSE CAST(false): boolean nullable. (exp2){code}
Then exp1 is considered as reduced. In the next step, by
ReduceExpressionsRule#simplifyPreservingType()[2], exp2 will be changed to
{code:java}
CAST(CASE WHEN x then true WHEN y then TRUE ELSE false): boolean nullable (exp3)
{code}
, 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]
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