【转】group_concat函数详解

转自： http://hchmsguo.iteye.com/blog/555543

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