SQL Server使用PIVOT与UNPIVOT实现行列转换

create table #table1
    (    id int ,code varchar(10) , name varchar(20) );
go

insert into #table1 ( id,code, name ) values ( 1, 'm1','a' ), ( 2,  'm2',null ), ( 3, 'm3', 'c' ), ( 4,  'm2','d' ), ( 5,  'm1','c' );
go

select * from #table1;

--方法一（推荐）
select PVT.code, PVT.a, PVT.b, PVT.c
      from #table1 pivot(count(id) for name in(a, b, c)) as PVT;

--方法二：使用 CTE 增强可读性
with P as (select * from #table1)
select PVT.code, PVT.a, PVT.b, PVT.c 
     from P        pivot(count(id) for name in(a, b, c)) as PVT;

declare @strCN nvarchar(100);
-- 先查询出要转为列的行数据，拼接列名字符串
select @strCN = isnull(@strCN + ',', '') + quotename(name) from #table1 group by name ;
print  @strCN  --‘[a],[c],[d]'

declare @SqlStr nvarchar(1000);
set @SqlStr = N'
select * from #table1 pivot ( count(ID) for name in (' + @strCN + N') ) as PVT';
exec ( @SqlStr );

create table #table1 (id int,
code varchar(10),
name1 varchar(20),
name2 varchar(20),
name3 varchar(20));
go
insert into #table1(id, name1, name2, code, name3)
values(1, 'm1', 'a1', 'a2', 'a3'),
    (2, 'm2', 'b1', 'b2', 'b3'),
    (4, 'm1', 'c1', 'c2', 'c3');
go
select * from #table1;

--方法一：直接使用源表
select PVT.id, PVT.code, PVT.name, PVT.val 
            from #table1 unpivot(val for name in(name1, name2, name3)) as PVT;

--方法二：结合 CTE 书写
with P as (select * from #table1)
select PVT.id, PVT.code, PVT.name, PVT.val 
            from P       unpivot(val for name in(name1, name2, name3)) as PVT;