如果你想删除重复的城市，相同的state_id（重复记录），你可以做到这一点，通过将它们分组city，并state_id使用MIN或MAX功能：
| ID | STATE_ID | CITY |
------------------------------
| 1 | 1 | city_one |
| 2 | 1 | city_two |
| 3 | 1 | city_one |
| 4 | 1 | city_two |
| 5 | 2 | city_one |
| 6 | 3 | city_three |
| 7 | 3 | city_one |
| 8 | 3 | city_three |
| 9 | 4 | city_four |
| 10 | 4 | city_five |
DELETE city_table
FROM city_table
LEFT JOIN
(SELECT MIN(id) AS IDs FROM city_table
GROUP BY city,state_id
)A
ON city_table.ID = A.IDs
WHERE A.ids IS NULL;
应用上述查询后，您的表将如下所示：
| ID | STATE_ID | CITY |
------------------------------
| 1 | 1 | city_one |
| 2 | 1 | city_two |
| 5 | 2 | city_one |
| 6 | 3 | city_three |
| 7 | 3 | city_one |
| 9 | 4 | city_four |
| 10 | 4 | city_five |
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