在MySQL中通过几列获取重复的行

Question

我正在尝试通过大表（接近18 000行）中的多个列搜索重复的行。问题是查询需要花费很多时间，我试过这个：

 SELECT * FROM table_name a, table_name b 
 WHERE a.col1 = b.col1 
 AND a.col2 = b.col2 
 AND a.col3 = b.col3
 AND a.col4 = b.col4 
 AND a.id <> b.id

和此：

SELECT *
FROM table_name 
WHERE col1 IN (
    SELECT col1 
    FROM table_name 
    GROUP BY col1 
    HAVING count(col1) > 1
    )
AND col2 IN (
    SELECT col2
    FROM table_name 
    GROUP BY col2
    HAVING count(col2) > 1
    )
AND col3 IN (
    SELECT col3
    FROM table_name 
    GROUP BY col3
    HAVING count(col3) > 1
    )
AND col4 IN (
    SELECT col4
    FROM table_name 
    GROUP BY col4
    HAVING count(col4) > 1
    )

他们都工作，但太慢了。有什么想法吗？

Answer 1

您可以尝试使用一个联合GROUP BY语句，如：

SELECT * FROM table_name
    GROUP BY col1, col2, col3, col4
    HAVING count(*) > 1

至少，它看起来会更清洁。

修改

要将所有结果作为上一列的子集返回：

SELECT *
FROM table_name 
WHERE col4 IN (
  SELECT col4
  FROM table_name 
  WHERE col3 IN (
    SELECT col3
    FROM table_name 
    WHERE col2 IN (
      SELECT col2
      FROM table_name
      WHERE col1 IN (
        SELECT col1
        FROM table_name
        GROUP BY col1
        HAVING count(col1) > 1
        )
      )
    )

从概念上讲，这应该能够以更快的执行时间为您提供所有结果。