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doc: correct subquery optimization examples for clarity (#20274) #20276

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Feb 13, 2025
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doc: correct subquery optimization examples for clarity (#20274) #20276

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2 changes: 1 addition & 1 deletion subquery-optimization.md
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Expand Up @@ -24,7 +24,7 @@ By default, subqueries use `semi join` mentioned in [Understanding TiDB Executio
In this case, `ALL` and `ANY` can be replaced by `MAX` and `MIN`. When the table is empty, the result of `MAX(EXPR)` and `MIN(EXPR)` is NULL. It works the same when the result of `EXPR` contains `NULL`. Whether the result of `EXPR` contains `NULL` may affect the final result of the expression, so the complete rewrite is given in the following form:

- `t.id < all (select s.id from s)` is rewritten as `t.id < min(s.id) and if(sum(s.id is null) != 0, null, true)`
- `t.id < any (select s.id from s)` is rewritten as `t.id < max(s.id) or if(sum(s.id is null) != 0, null, false)`
- `t.id > any (select s.id from s)` is rewritten as `t.id > max(s.id) or if(sum(s.id is null) != 0, null, false)`

## `... != ANY (SELECT ... FROM ...)`

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