Simplify IsNotNull and IsNull expression #6345
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comphead
reviewed
May 12, 2023
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| // a IS NOT NULL --> true, if a is not nullable | ||
| Expr::IsNotNull(expr) if !info.nullable(&expr)? => lit(true), |
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Thanks @byteink. would you mind adding more description? Why the simplification needed and what exactly problem it solves? is it a bug or something?
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create table test(a int not null);
select a is nullwe can convert it into
select falsebecause a is not null
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@comphead It is not a bug. I've added some descriptions.
alamb
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May 15, 2023
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This looks great -- thank you @byteink and @comphead and @jackwener
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Which issue does this PR close?
None
Rationale for this change
expr_non_null IS NOT NULLis always trueexpr_non_null IS NULLis always falseThey are a type of predicate that is either unnecessary or impossible.
By simplifying them, we can gain more opportunities for optimization.
For example：
SELECT * FROM t WHERE col_non_null IS NOT NULL--(Simplify)-->SELECT * FROM t WHERE TRUE--(EliminateFilter)-->SELECT * FROM tSELECT * FROM t WHERE col_non_null IS NULL--(Simplify)-->SELECT * FROM t WHERE FALSE--(EliminateFilter)--><EmptyRelation>Are these changes tested?
Yes
Are there any user-facing changes?
No