T-SQL 透视查询答案

【问题标题】：T-SQL Pivot queryT-SQL 透视查询
【发布时间】：2017-02-22 09:20:03
【问题描述】：

我有一个包含laserform名称和日期的表格，例如

我的表名为 myBWB_LaserForms

laserform   editwhen
LRAP1.lpw   2009-09-03 16:06:00.000
CON29R.lpw  2009-10-29 12:35:00.000
UN1.lpw     2010-03-02 11:38:00.000
UN244.lpw   2012-04-19 12:14:00.000
LT3.lpw     2013-01-02 11:00:00.000
LRAP1.lpw   2007-12-10 15:34:00.000

我要生成的是一份报告，其中左侧有激光形式的名称，顶部有年份，例如2004、2005、2006，然后每个相交的单元格都会计算该表单名称在该特定年份的记录数。

通常我会做类似的事情

select l.laserform,
(select count(*) from mybwb_laserforms l1 where l1.laserform=l.laserform and year(editwhen)=2004) AS [2004],
(select count(*) from mybwb_laserforms l2 where l2.laserform=l.laserform and year(editwhen)=2005) AS [2005],
(select count(*) from mybwb_laserforms l3 where l3.laserform=l.laserform and year(editwhen)=2006) AS [2006],
(select count(*) from mybwb_laserforms l4 where l4.laserform=l.laserform and year(editwhen)=2007) AS [2007]
from mybwb_laserforms l
group by l.laserform
order by l.laserform

但是我意识到这是非常可怕的 SQL，我应该对此更加聪明。

我一直在尝试学习如何使用枢轴功能，但我很难理解它。

此外，我发现的大多数示例似乎都对查询的列进行了硬编码 - 如果数据透视表可以是动态的并获得唯一的 year(editwhen) 值，那就太好了，这样我接下来就不必修改查询了一年和之后的一年。

【问题讨论】：

标签： tsql pivot

【解决方案1】：

总结一下吧。

select laserform,
sum(case when year(editwhen)=2004 then 1 else 0 end) AS [2004],
sum(case when year(editwhen)=2005 then 1 else 0 end) AS [2005],
sum(case when year(editwhen)=2006 then 1 else 0 end) AS [2006],
sum(case when year(editwhen)=2007 then 1 else 0 end) AS [2007]
from mybwb_laserforms
where year(editwhen) between 2004 and 2007
group by laserform
order by laserform

或动态

declare @Year int = year(GetDate());
declare @Years TABLE ([year] varchar(4));
insert into @Years values (@Year-12),(@Year-11),(@Year-10),(@Year-9);

declare @SQLSums varchar(max) = '';
select @SQLSums = @SQLSums +char(13)+', sum(case when year(editwhen)='+[year]+' then 1 else 0 end) AS ['+[year]+']'
from @Years;

DECLARE @SQL nvarchar(max) = 'select laserform'+ @SQLSums +'
from mybwb_laserforms
group by laserform
where year(editwhen) between '+cast(@Year-12 as varchar)+' and '+cast(@Year-9 as varchar)+'
order by laserform';

--select @SQL;
exec (@SQL);

【讨论】：