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

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)

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

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

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

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。

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

        ,16