mysql group_concat子句使用order by 进行字符串排序时，若字符串值为数字，排序错位，比如：
mysql> select `size_group_id`, group_concat(name order by name asc) as sizes from `basic_sizes` where `size_group_id` in (2, 1) group by `size_group_id`
-> ;
+---------------+-------------------------------------+
| size_group_id | sizes |
+---------------+-------------------------------------+
| 1 | 11,13,15,17,5,7,9 |
| 2 | 26,27,28,29,30,31,32,33,34,35,36,37 |
+---------------+-------------------------------------+
2 rows in set (0.00 sec)
解决方案1：order by name+0
mysql> select `size_group_id`, group_concat(name order by name+0 asc) as sizes from `basic_sizes` where `size_group_id` in (2, 1) group by `size_group_id`;
+---------------+-------------------------------------+
| size_group_id | sizes |
+---------------+-------------------------------------+
| 1 | 5,7,9,11,13,15,17 |
| 2 | 26,27,28,29,30,31,32,33,34,35,36,37 |
+---------------+-------------------------------------+
2 rows in set (0.01 sec)
解决方案2：order by length(name),name
mysql> select `size_group_id`, group_concat(name order by length(name),name asc) as sizes from `basic_sizes` where `size_group_id` in (2, 1) group by `size_group_id`;
+---------------+-------------------------------------+
| size_group_id | sizes |
+---------------+-------------------------------------+
| 1 | 5,7,9,11,13,15,17 |
| 2 | 26,27,28,29,30,31,32,33,34,35,36,37 |
+---------------+-------------------------------------+
2 rows in set (0.00 sec)
