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
,
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