矩陣置換@mysql

本文通過實例介紹了MySQL中的group_concat函數的使用方法，比如select group_concat(name) 。
MySQL中group_concat函數
完整的語法如下：
group_concat([DISTINCT] 要連接的字段 [Order BY ASC/DESC 排序字段] [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字段的值打印在一行，逗號分隔(默認) 
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字段的值打印在一行，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字段的值打印在一行， 
逗號分隔

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)

以id分組，把name字段的值打印在一行，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)