select * from rm_user_department

DELETE
FROM
    rm_user_department  --这里不能使用别名,如果使用别名会报错
WHERE
    (
        user_id,
        dep_id,
        user_type
    ) IN (

select a.userID,a.depId,a.user_type from ( -- 这里需要套一层a,如果去掉这个a,会报错: You can‘t specify target table ‘rm_user_department‘ for update in FROM clause

        SELECT
            user_id as userID,
            dep_id as depId,
            user_type --     COUNT(*)
        FROM
            rm_user_department
        GROUP BY
            user_id,
            dep_id,
            user_type
        HAVING
            COUNT(*) > 1
) a 
    )
AND id NOT IN (
SELECT b.id from ( -- 这里b和上面的a是同理
    SELECT
        MIN(tt.id) AS id
    FROM
        rm_user_department tt
    GROUP BY
        user_id,
        dep_id,
        user_type
    HAVING
        COUNT(*) > 1
) b
);