MySQL中删除重复数据只保留一条

忘是亡心i 2022-05-08 06:28 296阅读 0赞

用SQL语句,删除掉重复项只保留一条

在几千条记录里,存在着些相同的记录,如何能用SQL语句,删除掉重复的呢   
1、查找表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断

![复制代码][copycode.gif]

SELECT
        *
    FROM
        people
    WHERE
        peopleId IN (
            SELECT
                peopleId
            FROM
                people
            GROUP BY
                peopleId
            HAVING
                count(peopleId) > 1
        )

![复制代码][copycode.gif]

2、删除表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断，只留有rowid最小的记录

![复制代码][copycode.gif]

DELETE
    FROM
        people
    WHERE
        peopleName IN (
            SELECT
                peopleName
            FROM
                people
            GROUP BY
                peopleName
            HAVING
                count(peopleName) > 1
        )
    AND peopleId NOT IN (
        SELECT
            min(peopleId)
        FROM
            people
        GROUP BY
            peopleName
        HAVING
            count(peopleName) > 1
    )

![复制代码][copycode.gif]

3、查找表中多余的重复记录（多个字段）

![复制代码][copycode.gif]

SELECT
        *
    FROM
        vitae a
    WHERE
        (a.peopleId, a.seq) IN (
            SELECT
                peopleId,
                seq
            FROM
                vitae
            GROUP BY
                peopleId,
                seq
            HAVING
                count(*) > 1
        )

![复制代码][copycode.gif]

4、删除表中多余的重复记录（多个字段），只留有rowid最小的记录

![复制代码][copycode.gif]

DELETE
    FROM
        vitae a
    WHERE
        (a.peopleId, a.seq) IN (
            SELECT
                peopleId,
                seq
            FROM
                vitae
            GROUP BY
                peopleId,
                seq
            HAVING
                count(*) > 1
        )
    AND rowid NOT IN (
        SELECT
            min(rowid)
        FROM
            vitae
        GROUP BY
            peopleId,
            seq
        HAVING
            count(*) > 1
    )

![复制代码][copycode.gif]

5、查找表中多余的重复记录（多个字段），不包含rowid最小的记录

![复制代码][copycode.gif]

SELECT
        *
    FROM
        vitae a
    WHERE
        (a.peopleId, a.seq) IN (
            SELECT
                peopleId,
                seq
            FROM
                vitae
            GROUP BY
                peopleId,
                seq
            HAVING
                count(*) > 1
        )
    AND rowid NOT IN (
        SELECT
            min(rowid)
        FROM
            vitae
        GROUP BY
            peopleId,
            seq
        HAVING
            count(*) > 1
    )

![复制代码][copycode.gif]

6.消除一个字段的左边的第一位：

UPDATE tableName
    SET [ Title ]= RIGHT ([ Title ],(len([ Title ]) - 1))
    WHERE
        Title LIKE '村%'

7.消除一个字段的右边的第一位：

UPDATE tableName
    SET [ Title ]= LEFT ([ Title ],(len([ Title ]) - 1))
    WHERE
        Title LIKE '%村'

8.假删除表中多余的重复记录（多个字段），不包含rowid最小的记录

![复制代码][copycode.gif]

UPDATE vitae
    SET ispass =- 1
    WHERE
        peopleId IN (
            SELECT
                peopleId
            FROM
                vitae
            GROUP BY
                peopleId

![复制代码][copycode.gif]

源文件：[https://www.cnblogs.com/jiangxiaobo/p/6589541.html][https_www.cnblogs.com_jiangxiaobo_p_6589541.html]

[copycode.gif]: /images/20220508/06898f96cf394f50b1f6e780772d76de.png
[https_www.cnblogs.com_jiangxiaobo_p_6589541.html]: https://www.cnblogs.com/jiangxiaobo/p/6589541.html