从x左联接y中删除x.a在表y中不为空

Question

如何从表A中删除表B中不存在的记录？

我尝试过：

DELETE FROM
    x
LEFT JOIN
    y
ON
    x.image_hash IS NOT NULL IN y

Answer 1

适当使用EXISTS或NOT EXISTS子句。

DELETE FROM x WHERE <NOT> EXISTS (SELECT 1 FROM y WHERE y.<something> = x.<some_column> AND <some more conditions>