Simplify IsNotNull and IsNull expression#6345
Merged
Merged
Conversation
comphead
reviewed
May 12, 2023
| } | ||
|
|
||
| // a IS NOT NULL --> true, if a is not nullable | ||
| Expr::IsNotNull(expr) if !info.nullable(&expr)? => lit(true), |
Contributor
There was a problem hiding this comment.
Thanks @byteink. would you mind adding more description? Why the simplification needed and what exactly problem it solves? is it a bug or something?
Member
There was a problem hiding this comment.
create table test(a int not null);
select a is nullwe can convert it into
select falsebecause a is not null
Member
Author
There was a problem hiding this comment.
@comphead It is not a bug. I've added some descriptions.
alamb
approved these changes
May 15, 2023
Contributor
alamb
left a comment
alamb
left a comment
There was a problem hiding this comment.
This looks great -- thank you @byteink and @comphead and @jackwener
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
4 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
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