使用动态列出现选择

Question

使用如下表格：

name    country   state
-----   -------   -----
ana     usa        ca
paul    usa        wy
louis   can        ot
ana     usa        ca
john    can        al
paul    usa        wy
john    usa        ca
ana     usa        ca
louis   can        ot

我需要这样的结果：

country    state   ana   paul  louis  john  
--------   -----   ----  ----  -----  ----  
usa        ca       3     1     0      1
           wy       0     1     0      0
can        ot       0     0     2      0
           al       0     0     0      1

（使用动态列按名称计数出现次数，按国家和州分组）

有没有可能只用一句话来搭建？

Answer 1

如果你想要一个动态的方式：

样本数据

create table MyTable(
    name varchar(20),
    country varchar(20),
    state varchar(20)
)
insert into MyTable values
('ana', 'usa', 'ca'),
('paul', 'usa', 'wy'),
('louis', 'can', 'ot'),
('ana', 'usa', 'ca'),
('john', 'can', 'al'),
('paul', 'usa', 'wy'),
('john', 'usa', 'ca'),
('ana', 'usa', 'ca'),
('louis', 'can', 'ot');

使用 CROSSTAB 的解决方案

declare @sql1 as varchar(4000) = ''
declare @sql2 as varchar(4000) = ''
declare @sql3 as varchar(4000) = ''

select @sql1 = 
'select
    country
    ,state
'

select @sql2 = @sql2 +
'   ,sum(case when name = ''' + name + ''' then 1 else 0 end) as [' + name + ']' + char(10)
from (
    select distinct name from MyTable
)t
order by name

select @sql3 = 
'from MyTable
group by country, state
order by country, state desc
'

print (@sql1 + @sql2 + @sql3)
exec (@sql1 + @sql2 + @sql3)

Answer 2

需要pivot操作才能达到效果。

http://sqlfiddle.com/#!3/aae09/3

select country, state, 
       sum(case when name='ana' then 1 else 0 end) as ana,
       sum(case when name='paul' then 1 else 0 end) as paul,
       sum(case when name='john' then 1 else 0 end) as john,
       sum(case when name='louis' then 1 else 0 end) as louis
from table_name
group by country, state
order by country,state desc;