my sql 中group_concat函数使用

MySQL group_concat函数是典型的字符串连接函数
完整的语法如下：
group_concat([DISTINCT] 要连接的字段 [Order BY ASC/DESC 排序字段] [Separator '分隔符'])

基本查询

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)

例一：以id分组，把name字段的值打印在一行，逗号分隔(默认)

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) 

例二：以id分组，把name字段的值打印在一行，分号分隔

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)

 

例四：以id分组，把去冗余的name字段的值打印在一行，

逗号分隔

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) 

例五：以id分组，把name字段的值打印在一行，逗号分隔，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)