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mysql删除重复数据保留一条(SQL如何删除表中重复数据)


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

请留意红色部分

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
    )
复制代码

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
)
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执行上面的语句会现在的mysql中会提示:

执行报错:1093 - You can't specify target table 'student' for update in FROM clause 原因是:更新数据时使用了查询,而查询的数据又做了更新的条件,mysql不支持这种方式。 怎么规避这个问题? 再加一层封装,如下:

DELETE
FROM
    people
WHERE
    peopleName IN (
         SELECT
            peopleName
        FROM(
             SELECT
                peopleName
            FROM
                people
            GROUP BY
                peopleName
            HAVING
                count(peopleName) > 1
        ) a
    )
AND peopleId NOT IN (
    SELECT
            peopleName
    FROM(
        SELECT
            min(peopleId)
        FROM
            people
        GROUP BY
            peopleName
        HAVING
            count(peopleName) > 1
    ) b
)
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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
    )
复制代码

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
)
复制代码

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
)
复制代码

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%'
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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'

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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 tableName 
SET key = value WHERE key1 IN (
SELECT key1 FROM vitae GROUP BY peopleId)
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