Question

我尝试从表fe_users获取冗余的所有UID列表，然后运行我的DELETE命令删除它们。

e.g。我有这张桌子（fe_users）：

uid | pid | username
--------------
1   | 100 |  hans
2   | 100 |  karl
3   | 100 |  franz
4   | 100 |  karl
5   | 100 |  hans

这就是我选择所有重复的方式：

SELECT * FROM fe_users
WHERE uid NOT IN (
    SELECT uid  
    FROM fe_users
    WHERE pid=100
    GROUP BY username
    HAVING COUNT(username) > 1
)
AND username IN (
    SELECT username 
    FROM fe_users
    WHERE pid=100
    GROUP BY username
    HAVING COUNT(username) > 1
)

返回：

uid | pid | username
--------------------
5   | 100 |  hans
4   | 100 |  karl

现在我必须删除它们。

尝试＃1：

（提示：刚刚使用SELECT从上面的DELETE替换了DELETE * FROM fe_users WHERE uid NOT IN ( SELECT uid FROM fe_users WHERE pid=100 GROUP BY username HAVING COUNT(username) > 1 ) AND username IN ( SELECT username FROM fe_users WHERE pid=100 GROUP BY username HAVING COUNT(username) > 1 )

DELETE FROM fe_users
WHERE uid NOT IN (
    SELECT uid (
        SELECT uid
        FROM fe_users
        WHERE pid=100
        GROUP BY username
        HAVING COUNT(username) > 1
        )
    ) AS uid
AND username IN (
    SELECT username (
        SELECT username 
        FROM fe_users
        WHERE pid=100
        GROUP BY username
        HAVING COUNT(username) > 1
        )
    ) AS username;

响应：

您无法指定目标表＆＃39; fe_users＆＃39;用于FROM子句中的更新

尝试＃2

所以我尝试再使用一个选择，如this answer中建议的那样。

{{1}}

回复：

语法错误附近＆＃39; SELECT uid FROM fe_users WHERE pid = 0 GROUP BY usernam＆＃39;在第4行

我不知道如何做到这一点，我想知道MySQL开发人员通过实施这种无意义的限制来思考什么。

我是否必须使用PHP删除它？

Answer 1

您的查询似乎比必要的更复杂。我会去：

delete u
    from fe_users u join
         fe_users u2
         on u.pid = u2.pid and u.username = u2.username and
            u2.uid > u.uid
    where u.pid = 100;

这将删除具有相同pid和username的行且uid更大的所有行。您可以通过将delete u更改为select u.*来获取列表。

Answer 2

我的第二次尝试包含语法错误，因为错误输出已声明。我错过了FROM，还有其他一些错误。这是有效的查询：

const quadWidth = Math.PI / 2;     // area of effect PI/2 is 90 degree
const steps = radius / quadWidth; // number steps around the circle matches 1 pixel per step, 
const noiseAmpMax = 5;         // in pixels
const noiseWaveMoveSpeed = 2;  // speed of waves on circle in radians per second
const noiseWaveFreq = 16;      // how many waves per 360 deg

我希望MySQL开发人员能够解决这个问题，这样我们就不需要添加不必要的SELECTS了。

SQL - 删除表X中的所有重复条目

2 个答案: