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
)

 发现在mysql中会报错

错误信息：[Err] 1093 - You can't specify target table 'people' for update in FROM clause

于是查资料说是不能先select出同一表中的某些值，再update这个表(在同一语句中) 

上诉实例2在mysql会报错 mssql和oracle不会 可以改为：

DELETE
FROM
    people
WHERE
    peopleId NOT IN (
    SELECT
        peopleId
    FROM
        (
            SELECT
                max(b.peopleId) AS peopleId
            FROM
                `people` b
						
            GROUP BY
                b.peopleName
        ) b
)
AND time<1528560157

　　

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