MySQL中删除重复数据只保留一条

最新推荐文章于 2024-07-11 10:27:20 发布

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最新推荐文章于 2024-07-11 10:27:20 发布

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本文提供了一种使用SQL语句的方法来查找和删除数据库表中的重复记录。包括针对单个字段和多个字段的情况，并展示了如何仅保留rowid最小的记录。

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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

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

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
注：（这条语句会报错，查询和删除可能不能在同一条sql中）

    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
    )

3、查找表中多余的重复记录（多个字段）

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

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\

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
)

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

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
)

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

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

转：http://www.cnblogs.com/jiangxiaobo/p/6589541.html