sql - 将 SQL 表中的数据从行列转换为列行的好方法有哪些？

Question

将 SQL 表中的数据从行列转换为列行的好方法有哪些？

还允许在初始查询上应用过滤器/位置条件。

使用 SQL Server 2008。

现有表具有以下列：AID（nvarchar 唯一）ASID（nvarchar 唯一）里程碑（M1、M2、M3...M100）里程碑日期（日期时间）

转置数据如下：AID、ASID、M1 日期、M2 日期、M3 日期、M5 日期

Answer 1

如果您使用的是 SQL Server 2005+，那么您有几个选项可以转置数据。您可以实现PIVOT类似这样的功能：

select AID, ASID, 
  M1 as M1_Date, M2 as M2_Date, 
  M3 as M3_Date, M4 as M4_Date, M5 as M5_Date
from 
(
  select AID, ASID, Milestone,
    MilestoneDate
  from yourtable
  where AID = whatever -- other filters here
) src
pivot
(
  max(milestonedate)
  for milestone in (M1, M2, M3, M4, M5...)
) piv

或者您可以使用带有CASE语句的聚合函数：

select aid, 
  asid, 
  max(case when milestone = 'M1' then milestonedate else null end) M1_Date,
  max(case when milestone = 'M2' then milestonedate else null end) M2_Date,
  max(case when milestone = 'M3' then milestonedate else null end) M3_Date,
  max(case when milestone = 'M4' then milestonedate else null end) M4_Date
from yourtable
where AID = whatever -- other filters here 
group by aid, asid

milestone如果您有已知数量的值，则上述两个查询效果很好。但如果没有，那么你可以实现动态 sql 来转置数据。动态版本将与此类似：

DECLARE @cols AS NVARCHAR(MAX),
    @query  AS NVARCHAR(MAX),
    @colNames AS NVARCHAR(MAX),

select @cols = STUFF((SELECT distinct ',' + QUOTENAME(Milestone) 
                    from yourtable
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

select @colNames = STUFF((SELECT distinct ',' + QUOTENAME(Milestone+'_Date') 
                    from yourtable
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

set @query = 'SELECT AID, ASID,' + @colNames + ' from 
             (
                select AID, ASID, Milestone,
                  MilestoneDate
                from yourtable
                where AID = whatever -- other filters here 
            ) x
            pivot 
            (
                max(MilestoneDate)
                for Milestone in (' + @cols + ')
            ) p '

execute(@query)

Answer 2

这是一种相当通用的方法：

select 
aid, asid, 
max (case when milestone = 'M1' then milestonedate else null end) M1Date,
max (case when milestone = 'M2' then milestonedate else null end) M2Date,
max (case when milestone = 'M3' then milestonedate else null end) M3Date,
max (case when milestone = 'M5' then milestonedate else null end) M5Date
from
mytable
group by aid, asid