Mysql中关于 group_concat函数详解

2021-07-18 01:47:33

group_concat（）主要功能：能将相同的行组合起来

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('[', GROUP_CONCAT
(ROLE.Role_Name SEPARATOR '],['), ']')) AS ROLENAME
,(concat( '[', (
SELECT
GROUP_CONCAT
(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)
GROUP BY
EMPLOYEES.EMPID
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

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