group_concat函数详解

问了好多人，都不知道group_concat这个函数。

这个函数好啊，能将相同的行组合起来，省老事了。

MySQL中group_concat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

Sql代码


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分组，把name字段的值打印在一行，逗号分隔(默认)

Sql代码


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分组，把name字段的值打印在一行，分号分隔

Java代码


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分组，把去冗余的name字段的值打印在一行，

逗号分隔

Sql代码


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分组，把name字段的值打印在一行，逗号分隔，以name排倒序

Sql代码


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)

测试sql，项目中用到的。

Sql代码


SELECT

EMPLOYEES.EMPID

,EMPLOYEES.EMPNAME

,DEPARTMENTS.DEPARTMENTNAME

,EMPLOYEES.DEPTID

,EMPLOYEES.EMPPWD

,EMPLOYEES.INSIDEEMAIL

,EMPLOYEES.OUTSIDEEMAIL

,EMPLOYEES.DELEFLAG

,EMPLOYEES.EMPCLASS

,(CONCAT('[', <span style="color: #ff0000;">GROUP_CONCAT</span>

(ROLE.Role_Name SEPARATOR '],['), ']')) AS ROLENAME

,(concat( '[', (

SELECT

<span style="color: #ff0000;">GROUP_CONCAT</span>

(DEPARTMENTS.DEPARTMENTNAME separator '],[')

FROM

EMP_ROLE_DEPT

LEFT JOIN DEPARTMENTS

ON (

DEPARTMENTS.DEPARTMENTID = EMP_ROLE_DEPT.DEPTID

AND DEPARTMENTS.DELEFLAG = 0

)

GROUP BY

EMP_ROLE_DEPT.EMPID

HAVING

EMP_ROLE_DEPT.EMPID = EMPLOYEES.EMPID

),']')) AS DEPARTMENTRIGHT

FROM

EMPLOYEES

LEFT JOIN DEPARTMENTS

ON (

DEPARTMENTS.DEPARTMENTID = EMPLOYEES.DEPTID

AND DEPARTMENTS.DELEFLAG = 0

)

LEFT JOIN ROLE_EMP

ON (ROLE_EMP.EMP_ID = EMPLOYEES.EMPID)

LEFT JOIN ROLE

ON (ROLE_EMP.ROLE_ID = ROLE.ROLE_ID)

<span style="color: #ff0000;"> GROUP BY

EMPLOYEES.EMPID</span>

HAVING

EMPLOYEES.EMPID LIKE '%%'

AND EMPLOYEES.EMPNAME LIKE '%%'

AND EMPLOYEES.DELEFLAG = 0

AND (

EMPLOYEES.EMPCLASS = '1'

OR EMPLOYEES.EMPCLASS = '2'

)

AND EMPLOYEES.DEPTID = '001' LIMIT 0

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