Mysql 返回重复记录

我只想从表中返回重复的记录。在我的例子中，如果col1、col2、col3和col4中有多个记录具有相同的值，则记录是重复的

SELECT  m.*
FROM    (
        SELECT  col1, col2, col3, col4, COUNT(*)
        FROM    mytable
        GROUP BY
                col1, col2, col3, col4
        HAVING  COUNT(*) > 1
        ) md
JOIN    mytable m
ON      m.col1 = md.col1
        AND m.col2 = md.col2
        AND m.col3 = md.col3
        AND m.col4 = md.col4

如果要显示其他列，可以

将上述列加入表中：

SELECT t.*
     , dup.cnt
FROM yourTable t
    JOIN
      ( SELECT col1, col2, col3, col4
             , COUNT(*) AS cnt
        FROM yourTable
        GROUP BY col1, col2, col3, col4
        HAVING COUNT(*) > 1
      ) AS dup
      ON  t.col1 = dup.col1
      AND t.col2 = dup.col2
      AND t.col3 = dup.col3
      AND t.col4 = dup.col4

这难道不只是返回所有
col1、col2、col3、col4
都
notnull
的行吗？
SELECT t.*
     , dup.cnt
FROM yourTable t
    JOIN
      ( SELECT col1, col2, col3, col4
             , COUNT(*) AS cnt
        FROM yourTable
        GROUP BY col1, col2, col3, col4
        HAVING COUNT(*) > 1
      ) AS dup
      ON  t.col1 = dup.col1
      AND t.col2 = dup.col2
      AND t.col3 = dup.col3
      AND t.col4 = dup.col4