Mysql中关于 group_concat函数详解

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

1. 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)

1. 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

1. 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

1. 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

1. 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。

1. SELECT
2. EMPLOYEES.EMPID
3. ,EMPLOYEES.EMPNAME
4. ,DEPARTMENTS.DEPARTMENTNAME
5. ,EMPLOYEES.DEPTID
6. ,EMPLOYEES.EMPPWD
7. ,EMPLOYEES.INSIDEEMAIL
8. ,EMPLOYEES.OUTSIDEEMAIL
9. ,EMPLOYEES.DELEFLAG
10. ,EMPLOYEES.EMPCLASS
11. ,(CONCAT('[', <span style="color: #ff0000;">GROUP_CONCAT</span>
12. (ROLE.Role_Name SEPARATOR '],['), ']')) AS ROLENAME
13. ,(concat( '[', (
14. SELECT
15. <span style="color: #ff0000;">GROUP_CONCAT</span>
16. (DEPARTMENTS.DEPARTMENTNAME separator '],[')
17. FROM
18. EMP_ROLE_DEPT
19. LEFT JOIN DEPARTMENTS
20. ON (
21. DEPARTMENTS.DEPARTMENTID = EMP_ROLE_DEPT.DEPTID
22. AND DEPARTMENTS.DELEFLAG = 0
23. )
24. GROUP BY
25. EMP_ROLE_DEPT.EMPID
26. HAVING
27. EMP_ROLE_DEPT.EMPID = EMPLOYEES.EMPID
28. ),']')) AS DEPARTMENTRIGHT
29. FROM
30. EMPLOYEES
31. LEFT JOIN DEPARTMENTS
32. ON (
33. DEPARTMENTS.DEPARTMENTID = EMPLOYEES.DEPTID
34. AND DEPARTMENTS.DELEFLAG = 0
35. )
36. LEFT JOIN ROLE_EMP
37. ON (ROLE_EMP.EMP_ID = EMPLOYEES.EMPID)
38. LEFT JOIN ROLE
39. ON (ROLE_EMP.ROLE_ID = ROLE.ROLE_ID)
40. <span style="color: #ff0000;">    GROUP BY
41. EMPLOYEES.EMPID</span>
42. HAVING
43. EMPLOYEES.EMPID LIKE '%%'
44. AND EMPLOYEES.EMPNAME LIKE '%%'
45. AND EMPLOYEES.DELEFLAG = 0
46. AND (
47. EMPLOYEES.EMPCLASS = '1'
48. OR EMPLOYEES.EMPCLASS = '2'
49. )
50. AND EMPLOYEES.DEPTID = '001' LIMIT 0
51. ,16