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  • MySQL中删除重复数据只保留一条

    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

    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
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  • 原文地址:https://www.cnblogs.com/phpfensi/p/5599560.html
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