[jira] [Created] (IMPALA-7750) Additional FE optimizations for CASE expressions

["Paul Rogers (JIRA)" <ji...@apache.org>]

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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