MySQL自定义排序函数 field()

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1、mysql in 排序按in里面的顺序来排序

select * from table where id IN (3,6,9,1,2,5,8,7);

这样的情况取出来后，其实，id还是按1,2,3,4,5,6,7,8,9,排序的，但如果我们真要按IN里面的顺序排序怎么办？SQL能不能完成？是否需要取回来后再foreach一下？

其实可以这样

select * from table where id IN (3,6,9,1,2,5,8,7) order by field(id,3,6,9,1,2,5,8,7);

出来的顺序就是指定的顺序了

关于这种排序的效率，有文章指出：FIELD(str,str1,str2,str3,…)Returns the index (position) of str in the str1, str2, str3, … list. Returns 0 if str is not found.排序过程：把选出的记录的 id 在 FIELD 列表中进行查找，并返回位置，以位置作为排序依据。这样的用法，会导致 Using filesort，是效率很低的排序方式。除非数据变化频率很低，或者有长时间的缓存，否则不建议用这样的方式排序。作者建议在程序代码中自行排序。但是也有人说这种排序不会出现什么性能瓶颈具体还是自己测试一下吧。

2、其他实例：

mysql> select * from driver_log order by name;+--------+-------+------------+-------+| rec_id | name  | trav_date  | miles |+--------+-------+------------+-------+|      1 | Ben   | 2006-08-30 |   152 ||      9 | Ben   | 2006-09-02 |    79 ||      5 | Ben   | 2006-08-29 |   131 ||      8 | Henry | 2006-09-01 |   197 ||      6 | Henry | 2006-08-26 |   115 ||      7 | Suzi  | 2006-09-02 |   502 ||      2 | Suzi  | 2006-08-29 |   391 |+--------+-------+------------+-------+10 rows in set (0.00 sec)mysql> select * from driver_log order by field(name,'Suzi','Ben','Henry');+--------+-------+------------+-------+| rec_id | name  | trav_date  | miles |+--------+-------+------------+-------+|      2 | Suzi  | 2006-08-29 |   391 ||      7 | Suzi  | 2006-09-02 |   502 ||      1 | Ben   | 2006-08-30 |   152 ||      9 | Ben   | 2006-09-02 |    79 ||      5 | Ben   | 2006-08-29 |   131 ||      8 | Henry | 2006-09-01 |   197 ||      6 | Henry | 2006-08-26 |   115 |+--------+-------+------------+-------+10 rows in set (0.00 sec)mysql> select * from driver_log order by field(name,'Suzi','Ben');+--------+-------+------------+-------+| rec_id | name  | trav_date  | miles |+--------+-------+------------+-------+|     10 | Henry | 2006-08-30 |   203 ||      8 | Henry | 2006-09-01 |   197 ||      7 | Suzi  | 2006-09-02 |   502 ||      2 | Suzi  | 2006-08-29 |   391 ||      5 | Ben   | 2006-08-29 |   131 ||      9 | Ben   | 2006-09-02 |    79 ||      1 | Ben   | 2006-08-30 |   152 |+--------+-------+------------+-------+10 rows in set (0.00 sec)mysql> select * from driver_log order by field(name,'Suzi','Ben') desc;+--------+-------+------------+-------+| rec_id | name  | trav_date  | miles |+--------+-------+------------+-------+|      1 | Ben   | 2006-08-30 |   152 ||      9 | Ben   | 2006-09-02 |    79 ||      5 | Ben   | 2006-08-29 |   131 ||      2 | Suzi  | 2006-08-29 |   391 ||      7 | Suzi  | 2006-09-02 |   502 ||      8 | Henry | 2006-09-01 |   197 ||      6 | Henry | 2006-08-26 |   115 |+--------+-------+------------+-------+10 rows in set (0.00 sec)

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