mysql中not in，in，exists，not exists原理和區別

區別: in:spa where id in(x1,x2)等同於where id=x1 or id=x2select not in: 查詢 where id not in(x1,x2)等同於where id!=x1 and id!=x2 exists: where exists(select ......);select 子查詢有結果則「exists(select ......)」返回true,不

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