MySQL 优化实例
mysql>SELECT userId,leaveDttm, costTime, raid as layer FROM TongTianRecord as aWHERE times != 0 and raid!=0 and raid = (select max(raid) from TongTianRecord as b where a.userId=b.userId ) group by userId order by layer Desc , leaveDttm asc limit 50 -> ;+--------+---------------------+----------+-------+
| userId | leaveDttm | costTime | layer |
+--------+---------------------+----------+-------+
| 432676 | 2010-03-03 20:44:25 | 47271 | 142 |
| 437123 | 2010-03-07 19:40:43 | 38798 | 142 |
| 385063 | 2010-03-02 19:05:52 | 14772 | 140 |
| 370529 | 2010-03-11 10:00:40 | 68756 | 140 |
| 416174 | 2010-05-22 10:03:24 | 72971 | 133 |
| 385938 | 2010-06-07 13:47:52 | 28274 | 129 |
| 442027 | 2010-06-09 11:08:35 | 48048 | 128 |
| 107397 | 2010-01-09 23:58:35 | 9954 | 123 |
| 129437 | 2010-01-17 08:13:40 | 41907 | 123 |
| 227342 | 2010-02-17 12:19:09 | 6170 | 123 |
| 441531 | 2010-03-20 12:52:47 | 5901 | 123 |
| 180382 | 2010-04-07 21:53:42 | 19133 | 123 |
| 212991 | 2010-06-20 08:48:32 | 57859 | 123 |
| 252337 | 2010-07-23 00:41:53 | 4867 | 123 |
| 216937 | 2010-01-07 06:27:14 | 24580 | 122 |
|73227 | 2010-02-05 18:09:50 | 8336 | 122 |
| 187937 | 2010-03-18 23:55:45 | 7375 | 122 |
| 220040 | 2010-03-20 13:48:14 | 45294 | 122 |
| 185100 | 2010-05-06 02:34:09 | 13080 | 122 |
| 187953 | 2010-05-11 20:54:49 | 3571 | 122 |
| 118332 | 2010-05-20 19:19:37 | 9057 | 122 |
| 303014 | 2010-06-06 15:35:23 | 9638 | 122 |
| 218924 | 2010-07-14 19:53:41 | 93286 | 122 |
| 218689 | 2010-01-03 00:00:09 | 2999 | 121 |
| 245938 | 2010-01-17 19:39:56 | 13599 | 121 |
| 425601 | 2010-05-18 17:11:56 | 5007 | 121 |
| 217315 | 2010-05-22 09:33:52 | 45245 | 121 |
| 368088 | 2010-01-12 20:10:09 | 182014 | 120 |
| 125729 | 2010-01-19 22:25:11 | 2245 | 120 |
| 354352 | 2010-02-13 20:39:18 | 28959 | 120 |
| 126128 | 2010-03-21 18:00:46 | 2585 | 120 |
| 423356 | 2010-05-02 15:26:07 | 3718 | 120 |
| 408878 | 2010-05-22 11:43:47 | 3896 | 120 |
| 276298 | 2010-06-05 17:38:37 | 15662 | 120 |
| 406735 | 2010-06-14 00:36:41 | 9331 | 114 |
| 398012 | 2010-01-08 15:56:49 | 3703 | 103 |
| 238642 | 2010-01-12 18:36:37 | 18024 | 103 |
| 391747 | 2010-03-05 09:54:07 | 31989 | 103 |
| 393066 | 2010-03-10 17:37:59 | 11688 | 103 |
| 188250 | 2010-04-09 22:28:46 | 11168 | 103 |
| 421844 | 2010-05-13 09:13:20 | 32757 | 103 |
| 188049 | 2010-05-18 19:37:45 | 12703 | 103 |
| 403485 | 2010-05-23 16:20:20 | 8884 | 103 |
| 405829 | 2010-06-04 17:21:31 | 9288 | 103 |
| 432198 | 2010-06-07 06:26:58 | 21719 | 103 |
| 386609 | 2010-06-20 20:40:16 | 4943 | 103 |
| 447321 | 2010-07-04 08:18:14 | 56203 | 103 |
| 250245 | 2010-01-14 07:36:51 | 27718 | 102 |
| 255427 | 2010-02-01 17:25:28 | 15714 | 102 |
| 249995 | 2010-02-01 17:26:40 | 14328 | 102 |
+--------+---------------------+----------+-------+
50 rows in set (42 min 38.90 sec)
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