多对多的查询
表 Users
Uid UserName
1 user01
2 user02
3 user03
4 user04

表 Department
Did DepartmentName
1 dpt01
2 dpt02
3 dpt03

表 ManagerOfDepartment
Uid Did
1 1
1 2
2 1
3 1

我想得到如下结果，不知道 SQL 语句怎么写

Did DepartmentName Managers
1 dpt01 user01,user02,user03
2 dpt02 user01
3 dpt03 NULL

[解决办法]
给个例参考.

--带符号合并行列转换

--有表t，其数据如下：
a b
1 1
1 2
1 3
2 1
2 2
3 1
--如何转换成如下结果:
a b
1 1,2,3
2 1,2
3 1

create table tb
(
a int,
b int
)
insert into tb(a,b) values(1,1)
insert into tb(a,b) values(1,2)
insert into tb(a,b) values(1,3)
insert into tb(a,b) values(2,1)
insert into tb(a,b) values(2,2)
insert into tb(a,b) values(3,1)
go

if object_id( 'pubs..f_hb ') is not null
drop function f_hb
go

--创建一个合并的函数
create function f_hb(@a int)
returns varchar(8000)
as
begin
declare @str varchar(8000)
set @str = ' '
select @str = @str + ', ' + cast(b as varchar) from tb where a = @a
set @str = right(@str , len(@str) - 1)
return(@str)
End
go

--调用自定义函数得到结果：
select distinct a ,dbo.f_hb(a) as b from tb

drop table tb

--结果
a b
----------- ------
1 1,2,3
2 1,2
3 1

（所影响的行数为 3 行）


多个前列的合并
数据的原始状态如下：
ID PR CON OP SC
001 p c 差 6
001 p c 好 2
001 p c 一般 4
002 w e 差 8
002 w e 好 7
002 w e 一般 1
===========================
用SQL语句实现，变成如下的数据
ID PR CON OPS
001 p c 差(6),好(2),一般(4)
002 w e 差(8),好(7),一般(1)

if object_id( 'pubs..tb ') is not null
drop table tb
go

create table tb
(
id varchar(10),
pr varchar(10),
con varchar(10),
op varchar(10),
sc int
)

insert into tb(ID,PR,CON,OP,SC) values( '001 ', 'p ', 'c ', '差 ', 6)
insert into tb(ID,PR,CON,OP,SC) values( '001 ', 'p ', 'c ', '好 ', 2)

insert into tb(ID,PR,CON,OP,SC) values( '001 ', 'p ', 'c ', '一般 ', 4)
insert into tb(ID,PR,CON,OP,SC) values( '002 ', 'w ', 'e ', '差 ', 8)
insert into tb(ID,PR,CON,OP,SC) values( '002 ', 'w ', 'e ', '好 ', 7)
insert into tb(ID,PR,CON,OP,SC) values( '002 ', 'w ', 'e ', '一般 ', 1)
go

if object_id( 'pubs..test ') is not null
drop table test
go
select ID,PR,CON , OPS = op + '( ' + cast(sc as varchar(10)) + ') ' into test from tb

--创建一个合并的函数
if object_id( 'pubs..f_hb ') is not null
drop function f_hb
go
create function f_hb(@id varchar(10),@pr varchar(10),@con varchar(10))
returns varchar(8000)
as
begin
declare @str varchar(8000)
set @str = ' '
select @str = @str + ', ' + cast(OPS as varchar) from test where id = @id and @pr = pr and @con = con
set @str = right(@str , len(@str) - 1)
return(@str)
End
go

--调用自定义函数得到结果：
select distinct id ,pr , con , dbo.f_hb(id,pr,con) as OPS from test

drop table tb
drop table test

--结果
id pr con OPS
---------- ---------- ---------- -------------------
001 p c 差(6),好(2),一般(4)
002 w e 差(8),好(7),一般(1)

（所影响的行数为 2 行）


create table b
(col varchar(20))

insert b values ( 'a ')
insert b values ( 'b ')
insert b values ( 'c ')
insert b values ( 'd ')
insert b values ( 'e ')


declare @sql varchar(1024)
set @sql= ' '
select @sql=@sql+b.col+ ', ' from (select col from b) as b
set @sql= 'select ' ' '+@sql+ ' ' ' '
exec(@sql)

[解决办法]
--建函
Create Function F_TEST(@Did Int)
Returns Varchar(8000)
As
Begin
Declare @S Varchar(8000)
Select @S = ' '
Select @S = @S + ', ' + UserName From Users A Inner Join ManagerOfDepartment B On A.Uid = B.Uid Where B.Did = @Did Order By A.Uid
Select @S = Stuff(@S, 1, 1, ' ')
Return @S
End
GO
--用
Select *, dbo.F_TEST(Did) As Managers From Department

[解决办法]
--建境
Create Table Users
(Uid Int,
UserName Varchar(100))
Insert Users Select 1, 'user01 '
Union All Select 2, 'user02 '
Union All Select 3, 'user03 '
Union All Select 4, 'user04 '

Create Table Department
(Did Int,
DepartmentName Varchar(10))
Insert Department Select 1, 'dpt01 '
Union All Select 2, 'dpt02 '
Union All Select 3, 'dpt03 '

Create Table ManagerOfDepartment
(Uid Int,
Did Int)
Insert ManagerOfDepartment Select 1, 1
Union All Select 1, 2
Union All Select 2, 1
Union All Select 3, 1
GO
--建函
Create Function F_TEST(@Did Int)
Returns Varchar(8000)
As
Begin
Declare @S Varchar(8000)
Select @S = ' '
Select @S = @S + ', ' + UserName From Users A Inner Join ManagerOfDepartment B On A.Uid = B.Uid Where B.Did = @Did Order By A.Uid
Select @S = Stuff(@S, 1, 1, ' ')
Return @S
End
GO

--用
Select *, dbo.F_TEST(Did) As Managers From Department
--除境
Drop Table Users, Department, ManagerOfDepartment
Drop Function F_TEST
--果
/*
DidDepartmentNameManagers
1dpt01user01,user02,user03
2dpt02user01
3dpt03NULL
*/
[解决办法]
--建立一个函数
Create Function GetManagers(@Did Int)
Returns Varchar(2000)
As
Begin
Declare @S Varchar(2000)
Select @S = ' '
Select @S = @S + ', ' + UserName From Users A Inner Join ManagerOfDepartment B On A.Uid = B.Uid Where B.Did = @Did Order By A.Uid
Select @S = Stuff(@S, 1, 1, ' ')
Return @S
End
GO
--输出
Select *, dbo.GetManagers(Did) As Managers From Department
[解决办法]
---创建函数
Create Function fnMerge(@Did varchar(10))
Returns Varchar(8000)
As
Begin
Declare @sql Varchar(8000)
Set @sql= ' '
Select @sql=@sql+ ', '+A.UserName From Users A
Inner Join ManagerOfDepartment B On A.Uid=B.Uid And B.Did=@Did
Return Stuff(@sql,1,1, ' ')
End
Go

---调用自定义函数
Select
Did,
DepartmentName,
dbo.fnMerge(Did) As Managers
From
Department
Order By Did