sql server多重行列转置的优化

将表1转化成表2：

               表1

               表2

得到表2的结果，需要经过多次pivot转换，再经union连接到一起，代码如下：

select id, type,sum([1]) [1],sum([2]) [2],sum([3]) [3],sum([4]) [4] from
(
    select 'a' as type, * from   Table_1
    pivot(sum(a)  for p in([1],[2],[3],[4])) as a 
union all
    select 'b' as type,* from   Table_1
    pivot(sum(b)  for p in([1],[2],[3],[4])) as b
union all
    select 'c'  as type,* from   Table_1
    pivot(sum(c)  for p in([1],[2],[3],[4])) as c
union all
    select 'd'  as type,* from   Table_1
    pivot(sum(d)  for p in([1],[2],[3],[4])) as d
) t1
group by id,type
order by id,type

此时代码看起来比较多，如果需要n多次pivot转换，代码过于繁多。

此时，可通过定义一个变量，以拼字符串的形式，来代替繁多的代码：

declare @str varchar(8000)  
set @str = ''
select  @str = @str + ' SELECT '''+ NAME + ''' AS TYPE,* FROM Table_1 pivot(SUM('+ NAME +') 
        for p in ([1],[2],[3],[4])) as '+ NAME +' union ALL ' 
        from syscolumns 
        where object_id('Table_1') = id AND NAME <> 'P' AND NAME <> 'ID'
select @str = left(@str,len(@str)-len('union ALL'))
select @str ='select id, type,sum([1]) [1],sum([2]) [2],sum([3]) [3],sum([4]) [4] from ('+ @str +') t1 group by id,type order by id,type'
exec (@str)

两种方法得出的结果是一样的，只是后者代码更为简洁。