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我所做的是创建一个名为 Rent2 的临时表来存放我的客户注册的所有重复模块，然后在删除临时表之前执行删除内部连接语句。

但是完成后总会有一个剩余的副本。我在这里做错了什么？

CREATE  TABLE IF NOT EXISTS `tblRent2` (
  `IdRent` INT(11) NOT NULL)
ENGINE = InnoDB;

INSERT INTO tblRent2 (SELECT IdRent FROM tblRent WHERE IdModule = 1 GROUP BY IdClient HAVING COUNT(IdModule) > 1);
INSERT INTO tblRent2 (SELECT IdRent FROM tblRent WHERE IdModule = 2 GROUP BY IdClient HAVING COUNT(IdModule) > 1);
INSERT INTO tblRent2 (SELECT IdRent FROM tblRent WHERE IdModule = 3 GROUP BY IdClient HAVING COUNT(IdModule) > 1);
INSERT INTO tblRent2 (SELECT IdRent FROM tblRent WHERE IdModule = 4 GROUP BY IdClient HAVING COUNT(IdModule) > 1);
INSERT INTO tblRent2 (SELECT IdRent FROM tblRent WHERE IdModule = 5 GROUP BY IdClient HAVING COUNT(IdModule) > 1);
INSERT INTO tblRent2 (SELECT IdRent FROM tblRent WHERE IdModule = 6 GROUP BY IdClient HAVING COUNT(IdModule) > 1);
INSERT INTO tblRent2 (SELECT IdRent FROM tblRent WHERE IdModule = 999 GROUP BY IdClient HAVING COUNT(IdModule) > 1);

DELETE r.* FROM tblRent r INNER JOIN tblRent2 r2 ON 
r.idRent = r2.idRent;

SELECT * FROM tblRent2;

DROP TABLE tblRent2;

原始表如下所示：

IdRent | IDClient  | IdModule
1      |  30       |   999
2      |  30       |   999
3      |  31       |   1
4      |  31       |   1

这些都是主键。

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2 回答 2

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一个更好的问题是你为什么要使用临时表？

只需将表连接到自身：

DELETE r2
FROM tblRent r
JOIN tblRent r2
    ON r.IDClient = r2.IDClient
    AND r.IdModule = r2.IdModule
    AND r.idRent < r2.idRent

这也将清理三重，总是留下最低的行idRent。

一个关键点（请原谅双关语）是额外的连接条件r.idRent < r2.idRent，它防止行连接到自身（通过具有不相等的 id），并选择最后添加的行进行删除（通过强制一个 id 小于另一个）。使用r.idRent != r2.idRent会导致两个重复项都被删除。

于 2013-08-29T21:50:53.393 回答
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我认为您的删除查询有缺陷。删除不应该在 delete 关键字之后需要星号。您可以使用此查询。

DELETE FROM tblRent WHERE idRent in (SELECT IdRent FROM tblRent2);
于 2013-08-29T21:47:43.457 回答