Question

我很难成功搜索到这一点，因为我还没有想出一个描述我想做什么的搜索字符串，如果已经涵盖了这一点，我会道歉。

我有一张表，其中包含合约编号，开始日期，序列号和日期戳。这些是很多：很多。

我想要实现的目标是返回每个合同编号的开始日期，其中包含最大数量的唯一序列号和最新的日期戳，其中该开始日期有效。

我认为这对T-SQL专家来说是显而易见的，只返回一个具有最多序列号的合同号。谁能告诉我我做错了什么？

SELECT TOP (1) 
   [Contract ID], [Item Begin Date] AS Start_Date, 
   COUNT([Serial Number]) AS CountSerials, 
   Datestamp
FROM
   SourceTable
GROUP BY 
   [Contract ID], [Item Begin Date], Datestamp
HAVING      
   ([Item Begin Date] > CONVERT(DATETIME, '1900-01-01 00:00:00', 102))
ORDER BY 
   CountSerials DESC, Datestamp DESC

干杯，亚历

Answer 1

您可以将其放入临时表中（不使用TOP（1）或oder）：我在这个过程中更改了一些表名，

    if exists (select * from tempdb.sys.tables where name = '##tmp')
  drop table ##tmp

  SELECT * into ##tmp
  from 
  (
  select 
   [Contract_ID], [Begin_Date] AS Start_Date, 
   COUNT([serials]) AS CountSerials, 
   Datestamp
FROM
   SourceTable
GROUP BY 
   [Contract_ID], [begin_date], Datestamp
HAVING      
   [begin_date] > CONVERT(DATETIME, '1900-01-01 00:00:00', 102)
   ) a

   select contract_id,Start_Date, max(countserials) as MAXCOUNT, Datestamp  from ##tmp
   group by contract_id,Start_Date,Datestamp

Answer 2

您可以使用聚合执行子查询并从中提取所需的结果：

SELECT distinct *
FROM
(
     Select
     [Contract ID], [Item Begin Date] AS Start_Date, 
     COUNT([Serial Number]) OVER(PARTITION BY [Contract ID]) AS CountSerials, 
     datestamp,
     MAX(Datestamp) OVER (PARTITION BY [Contract ID]) maxdatestamp
     FROM
        SourceTable
     WHERE      
        ([Item Begin Date] > CONVERT(DATETIME, '1900-01-01 00:00:00', 102))
) x
WHERE 
datestamp=maxdatestamp

T-SQL根据另一个字段返回前一个字段

2 个答案: