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*fromaa;
+------+------+
| 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
selectid,group_concat(name)fromaagroupbyid;
+------+--------------------+
| 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
selectid,group_concat(distinctname)fromaagroupbyid;
+------+-----------------------------+
| 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
selectid,group_concat(nameorderbynamedesc)fromaagroupbyid;
+------+---------------------------------------+
| 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('[',"color: #ff0000;">GROUP_CONCAT
(ROLE.Role_Name SEPARATOR '],['),']'))ASROLENAME
,(concat( '[', (
SELECT
"color: #ff0000;">GROUP_CONCAT
(DEPARTMENTS.DEPARTMENTNAME separator '],[')
FROM
EMP_ROLE_DEPT
LEFTJOINDEPARTMENTS
ON(
DEPARTMENTS.DEPARTMENTID = EMP_ROLE_DEPT.DEPTID
ANDDEPARTMENTS.DELEFLAG = 0
)
GROUPBY
EMP_ROLE_DEPT.EMPID
HAVING
EMP_ROLE_DEPT.EMPID = EMPLOYEES.EMPID
),']'))ASDEPARTMENTRIGHT
FROM
EMPLOYEES
LEFTJOINDEPARTMENTS
ON(
DEPARTMENTS.DEPARTMENTID = EMPLOYEES.DEPTID
ANDDEPARTMENTS.DELEFLAG = 0
)
LEFTJOINROLE_EMP
ON(ROLE_EMP.EMP_ID = EMPLOYEES.EMPID)
LEFTJOINROLE
ON(ROLE_EMP.ROLE_ID = ROLE.ROLE_ID)
"color: #ff0000;">GROUPBY
EMPLOYEES.EMPID
HAVING
EMPLOYEES.EMPID LIKE'%%'
ANDEMPLOYEES.EMPNAMELIKE'%%'
ANDEMPLOYEES.DELEFLAG = 0
AND(
EMPLOYEES.EMPCLASS = '1'
OREMPLOYEES.EMPCLASS ='2'
)
ANDEMPLOYEES.DEPTID ='001'LIMIT 0
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