mysql模拟rownum的一个方法

mysql> select * from t2;
+----+---------------------+
| id | d                   |
+----+---------------------+
|  1 | 2015-08-02 15:13:59 |
|  3 | 2015-08-05 16:56:23 |
|  4 | 2015-08-05 16:56:24 |
|  6 | 2015-08-05 16:56:26 |
|  7 | 2015-08-05 16:56:28 |
|  8 | 2015-08-05 16:56:29 |
+----+---------------------+
6 rows in set (0.00 sec)

mysql> set @x=0;
Query OK, 0 rows affected (0.00 sec)

mysql> select @x:=ifnull(@x,0)+1 as rownum,d as time from t2;
+--------+---------------------+
| rownum | time                |
+--------+---------------------+
|      1 | 2015-08-02 15:13:59 |
|      2 | 2015-08-05 16:56:23 |
|      3 | 2015-08-05 16:56:24 |
|      4 | 2015-08-05 16:56:26 |
|      5 | 2015-08-05 16:56:28 |
|      6 | 2015-08-05 16:56:29 |
+--------+---------------------+
6 rows in set (0.00 sec)