有什么好的方法可以将SQL表中的数据从行列转换为列行? [英] What are some good ways to transpose data in a SQL table from row-columns to column-rows?

问题描述

将SQL表中的数据从行列转换为列行的一些好方法是什么?

What are some good ways to transpose data in a SQL table from row-columns to column-rows?

还允许在初始查询中应用过滤器/条件.

Also allowing filters/where conditions to be applied on the initial query.

使用SQL Server 2008.

Using 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)

Existing table has following Columns: AID (nvarchar unique) ASID (nvarchar unique) Milestone (M1, M2, M3...M100) MilestoneDate (datetime)

转置数据如下: AID，ASID，M1日期，M2日期，M3日期，M5日期

Transposed data as follows: AID, ASID, M1 Date, M2 Date, M3 Date, M5 Date

推荐答案

如果您使用的是SQL Server 2005+，则可以使用一些选项来转置数据.您可以实现类似于以下内容的PIVOT函数:

If you are using SQL Server 2005+, then you have a few options to transpose the data. You can implement the PIVOT function similar to this:

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

或者您可以在CASE语句中使用聚合函数:

Or you can use an aggregate function with a CASE statement:

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

如果您具有已知数量的milestone值，则上述两个查询非常有用.但是，如果没有，则可以实现动态sql来转置数据.动态版本将与此类似:

The above two queries work great if you have a known number of milestone values. But if not, then you can implement dynamic sql to transpose the data. The dynamic version would be similar to this:

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)

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