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mysql> select * from tags;
+-------+-------+
| docid | tagid |
+-------+-------+
| 1 | 1 |
| 1 | 3 |
| 1 | 5 |
| 1 | 7 |
| 2 | 2 |
| 2 | 4 |
| 2 | 6 |
| 3 | 15 |
| 4 | 7 |
| 4 | 40 |
+-------+-------+
10 rows in set (0.07 sec)
mysql> set @num=0;
Query OK, 0 rows affected (0.00 sec)
mysql> select @num:=@num+1,docid,tagid from tags;
+--------------+-------+-------+
| @num:=@num+1 | docid | tagid |
+--------------+-------+-------+
| 1 | 1 | 1 |
| 2 | 1 | 3 |
| 3 | 1 | 5 |
| 4 | 1 | 7 |
| 5 | 2 | 2 |
| 6 | 2 | 4 |
| 7 | 2 | 6 |
| 8 | 3 | 15 |
| 9 | 4 | 7 |
| 10 | 4 | 40 |
+--------------+-------+-------+
10 rows in set (0.01 sec)
mysql>
@num 就是rownum