[jira] [Created] (CALCITE-7294) Simplify arguments to IS [NOT] NULL whenever possible

["Stamatis Zampetakis (Jira)" <ji...@apache.org>]

Stamatis Zampetakis created CALCITE-7294:
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             Summary: Simplify arguments to IS [NOT] NULL whenever possible
                 Key: CALCITE-7294
                 URL: https://issues.apache.org/jira/browse/CALCITE-7294
             Project: Calcite
          Issue Type: Improvement
          Components: core
            Reporter: Stamatis Zampetakis


Currently there are few cases where {{RexSimplify}} bails out when attempting to simplify an IS NULL/IS NOT NULL expression:
 * [https://github.com/apache/calcite/blob/31a23f38092c185ef0faf19f770c1de8625db0e8/core/src/main/java/org/apache/calcite/rex/RexSimplify.java#L1159]

 * [https://github.com/apache/calcite/blob/31a23f38092c185ef0faf19f770c1de8625db0e8/core/src/main/java/org/apache/calcite/rex/RexSimplify.java#L1190]

It seems possible though to simplify the arguments and retain the IS NULL/IS NOT NULL expression.

{+}Example{+}:
Currently {{COALESCE(age + 0, year) IS NULL}} cannot be simplified and is returned as is. However, we could simplify the expression to {{COALESCE(age, year) IS NULL}}.

This improvement mainly affects IS NULL and IS NOT NULL simplification when the argument is an function/operator with:
 * [custom nullability|https://github.com/apache/calcite/blob/31a23f38092c185ef0faf19f770c1de8625db0e8/core/src/main/java/org/apache/calcite/rex/RexSimplify.java#L1280] (i.e., CAST, ITEM)
 * {{Strong.Policy}} other than {{ANY}} and {{NOT_NULL}}



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