mysql - 使用mysql : How to add unique id for the same data in another colmun

Question

如何将唯一 ID 插入 car_id 列，如下表所示？

|car_id|     CarId  |
+------+------------+
|  1   |      1234  |
|  1   |      1234  |
|  1   |      1234  |
|  2   |      5678  |
|  2   |      5678  |
|  2   |      5678  |
|  3   |    9101112 |

Answer 1

使用变量:

   SELECT CarId, 
          @seq := IF(@cid = CarId, @seq,
                    IF(@cid := CarId, @seq + 1, @seq + 1)) AS car_id
   FROM mytable
   CROSS JOIN (SELECT @seq := 0, @cid := 0) AS vars 
   ORDER BY CarId

Demo here