MYSQL 刪除重複的數據

用SQL語句,刪除掉重複項只保留一條

在幾千條記錄裏,存在着些相同的記錄,如何能用SQL語句,刪除掉重複的呢

請留意紅色部分

一、查找表中多餘的重複記錄，重複記錄是根據單個字段（peopleId）來判斷

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

二、刪除表中多餘的重複記錄，重複記錄是根據單個字段（peopleId）來判斷，只留有rowid最小的記錄

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
)
複製代碼

執行上面的語句會如今的mysql中會提示：

執行報錯：1093 - You can't specify target table 'student' for update in FROM clause 緣由是：更新數據時使用了查詢，而查詢的數據又作了更新的條件，mysql不支持這種方式。 怎麼規避這個問題？ 再加一層封裝，以下：

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
)
複製代碼

三、查找表中多餘的重複記錄（多個字段）

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

四、刪除表中多餘的重複記錄（多個字段），只留有rowid最小的記錄

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
)
複製代碼

五、查找表中多餘的重複記錄（多個字段），不包含rowid最小的記錄

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
)
複製代碼

6.消除一個字段的左邊的第一位：

UPDATE tableName 
    SET [ Title ]= RIGHT ([ Title ],(len([ Title ]) - 1))
WHERE
    Title LIKE '村%'
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7. 消除一個字段的右邊的第一位：

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

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8.假刪除表中多餘的重複記錄（多個字段），不包含rowid最小的記錄

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

若是相似與上面的方法，請求留意，是否須要將條件再進行一次包含。

以上轉載:blog.csdn.net/u014723529/…