MySQL连接字段结果集

使用concat("one", " ", "three") 可以连接字符串
为 one three

mysql> select concat("one", " ", "three") as num;
+-----------+
| num       |
+-----------+
| one three |
+-----------+
1 row in set (0.00 sec)

group_concat('field name' separator ',')

mysql> select group_concat(id separator ',') as ids from users;
+-----------+
| ids       |
+-----------+
| 1,2,3,4,5 |
+-----------+
1 row in set (0.00 sec)