Paul Rogers created IMPALA-7750:
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Summary: Additional FE optimizations for CASE expressions
Key: IMPALA-7750
URL: https://issues.apache.org/jira/browse/IMPALA-7750
Project: IMPALA
Issue Type: Improvement
Components: Frontend
Affects Versions: Impala 3.0
Reporter: Paul Rogers
The current FE {{CASE}} rewrite code in
{{SimplifyConditionalsRule.simplifyCaseExpr()}} misses some opportunities for
optimizations. If these rules are implemented, then the ad-hoc rules for
several other functions can be removed.
{code:sql}
CASE WHEN NULL IS NULL THEN 10 ELSE 20 END
{code}
Should be rewritten to just {{10}} since the expression is always true.
(Currently the expression is not rewritten.)
The same issue occurs for the inverse:
{code:sql}
CASE WHEN 10 IS NULL THEN 10 ELSE 20 END
{code}
Fix these and we can remove the ad-hoc rules for {{NULLIF}} and aliases in
{{rewriteNullIfFn()}}.
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