mysql - 如何在 my-sql 中从一行中删除“无重复”记录

Question

例如，如果我有

+------------+-------------+
| something_1| something_2 |
+------------+-------------+
| 1          | a           |
| 2          | b           |
| 3          | a           |
| 4          | c           |
| 5          | b           |
| 6          | a           |
| 6          | d           |
| 6          | e           |
+------------+-------------+

我想要这个，删除不重复的数据：

+-------------+
| something_2 |
+-------------+
| a           |
| b           |    
+-------------+

谢谢，我想要它在mysql中，请

Answer 1

这只会给你重复的字段：

SELECT something_2 FROM mytable
GROUP BY something_2
HAVING COUNT(*) > 1

Answer 2

假设您的表有一个主键，请执行以下操作：

DELETE FROM my_table WHERE prim_key IN (SELECT prim_key FROM my_table
GROUP BY something_2
HAVING COUNT(*) > 1)