mysql刪除重復數據只保留id最大一條記錄

目的： 一張表，表名 credit_user

相同的 user_code有多條重復數據，現在只保留一條數據

一：首先是這么想的

DELETE
FROM
    credit_user
WHERE
    user_code IN (
        SELECT
            user_code
        FROM
            credit_user
        GROUP BY
            user_code
        HAVING
            count(user_code) > 1
    ) and  id NOT IN (
        SELECT
            min(id)
        FROM
            credit_user
        GROUP BY
            user_code
        HAVING
            count(user_code) > 1
    );

 

發現在mysql中會報錯

錯誤信息：[Err] 1093 - You can't specify target table 'credit_user' for update in FROM clause

於是查資料說是不能先select出同一表中的某些值，再update這個表(在同一語句中) 

二：正確寫法

DELETE
FROM
    credit.credit_user
WHERE
    user_code IN (
        SELECT * FROM (
        SELECT
            user_code
        FROM
            credit_user
        GROUP BY
            user_code
        HAVING
            count(user_code) > 1
          ) b
    ) and  id NOT IN (
        SELECT * FROM (
        SELECT
            min(id)
        FROM
            credit_user
        GROUP BY
            user_code
        HAVING
            count(user_code) > 1
          ) c
    );

 

也就是說將select出的結果再通過中間表select一遍，這樣就規避了錯誤。注意，這個問題只出現於mysql