MySQL中group_concat函式
完整的語法如下：
group_concat([DISTINCT] 要連線的欄位 [Order BY ASC/DESC 排序欄位] [Separator '分隔符'])

基本查詢

mysql> select * from aa;
 +------+------+
 | id| name |
 +------+------+
 |1 | 10|
 |1 | 20|
 |1 | 20|
 |2 | 20|
 |3 | 200  |
 |3 | 500  |
 +------+------+
 6 rows in set (0.00 sec)

以id分組，把name欄位的值列印在一行，逗號分隔

mysql> select id,group_concat(name) from aa group by id;
 +------+--------------------+
 | id| group_concat(name) |
 +------+--------------------+
 |1 | 10,20,20|
 |2 | 20 |
 |3 | 200,500|
 +------+--------------------+
 3 rows in set (0.00 sec)

以id分組，把name欄位的值列印在一行，分號分隔

mysql> select id,group_concat(name separator ';') from aa group by id;
 +------+----------------------------------+
 | id| group_concat(name separator ';') |
 +------+----------------------------------+
 |1 | 10;20;20 |
 |2 | 20|
 |3 | 200;500  |
 +------+----------------------------------+
 3 rows in set (0.00 sec)
 

以id分組，把去冗餘的name欄位的值列印在一行，

mysql> select id,group_concat(distinct name) from aa group by id;
 +------+-----------------------------+
 | id| group_concat(distinct name) |
 +------+-----------------------------+
 |1 | 10,20|
 |2 | 20  |
 |3 | 200,500 |
 +------+-----------------------------+
 3 rows in set (0.00 sec)
 

以id分組，把name欄位的值列印在一行，逗號分隔，以name排倒序

mysql> select id,group_concat(name order by name desc) from aa group by id;
 +------+---------------------------------------+
 | id| group_concat(name order by name desc) |
 +------+---------------------------------------+
 |1 | 20,20,10  |
 |2 | 20|
 |3 | 500,200|
 +------+---------------------------------------+
 3 rows in set (0.00 sec)