Question

我有一个跟踪文件版本历史记录的表，并希望构建一个查询来报告每个文件的最新版本。

当前表格结构：

fileID   fileName   fileVersion
 1        fileA      1.0.0
 2        fileB      1.0.0
 3        fileA      1.0.1
 4        fileC      1.0.0
 5        fileC      1.0.0
 6        fileA      1.0.2

我想要的是什么：

fileID   fileName   fileVersion   currentVersion
 1        fileA      1.0.0         
 2        fileB      1.0.0         current
 3        fileA      1.0.1
 4        fileC      1.0.0
 5        fileC      1.0.1         current
 6        fileA      1.0.2         current

较旧的文件版本可以为NULL，也可以使用不同的字符串（旧版，旧版等）列出。

我能够使用MAX（Version）构建一个子查询来列出当前版本，并尝试在带有Exists或In的CASE语句中使用它来创建新列，但无法使其工作。

Select t.*,
CASE When t.fileID Exists (sub query) Then 'current' Else NULL End As currentVersion
From t

基本上，我可以返回所有结果，我可以单独返回最近的版本，但我正在寻找有关如何一起使用这两个查询来创建currentVersion列的帮助。

Answer 1

您可以使用窗口函数Row_Number（）

Declare @YourTable table (FileID int,fileName varchar(50),fileVersion varchar(50) )
Insert Into @YourTable values
(1,'fileA','1.0.0'),
(2,'fileB','1.0.0'),
(3,'fileA','1.0.1'),
(4,'fileC','1.0.0'),
(5,'fileC','1.0.1'),
(6,'fileA','1.0.2')

Select * 
      ,currentVersion_A =case when Row_Number() over (Partition By FileName Order by FileID desc) = 1 then 'Current' else '' end
      ,currentVersion_B =case when Row_Number() over (Partition By FileName Order by FileVersion desc) = 1 then 'Current' else '' end
      ,currentVersion_C =case when Row_Number() over (Partition By FileName Order by Cast(ParseName(FileVersion,3 ) as Int) desc,Cast(ParseName(FileVersion,2) as Int) desc,Cast(ParseName(FileVersion,1) as Int) desc) = 1 then 'Current' else '' end 
 from @YourTable
 Order by FileID

-- You have 3 options on how to determine Current (you know your data better than we do)
-- Use currentVersion_A IF FileID is an Identity() and each new version is added to the table
-- Use currentVersion_B IF and ONLY IF version will be 0 and 9
-- Use currentVersion_C As suggested by @HABO which is SMARTER provided the pattern is consistent

返回

FileID      fileName    fileVersion currentVersion
1           fileA       1.0.0   
2           fileB       1.0.0       Current
3           fileA       1.0.1   
4           fileC       1.0.0   
5           fileC       1.0.1       Current
6           fileA       1.0.2       Current

创建新文本列以标识最新文件版本

1 个答案: