SQL查询根据条件选择不同的列

Answer 1

这将从您提供的示例数据中返回您想要的输出：

SELECT 
    t1.CompanyId
    ,t1.EmployeeId
    ,StartDate  = FORMAT(ISNULL(DATEFROMPARTS(YEAR(StartDate), min(t2.month), 1), StartDate), 'MM/dd/yyyy')
    ,EndDate    = FORMAT(
                    ISNULL(
                        DATEFROMPARTS(YEAR(enddate), max(t2.month), 1)
                        ,DATEADD(dd, -DATEPART(dd, enddate) + 1, enddate)
                    )
                    , 'MM/dd/yyyy')
    ,ISNULL(Allmonths, value) as Final
FROM [Table1] t1
INNER JOIN [Table2] t2 on t1.employeeid = t2.employeeid
                    AND t1.CompanyId = t2.CompanyId
                    AND (   (t2.allmonths IS NOT NULL) 
                            OR (t2.month BETWEEN DATEPART(MM, startdate) AND DATEPART(MM, enddate))
                        )
GROUP BY 
    t1.CompanyId
    ,t1.EmployeeId
    ,StartDate
    ,EndDate
    ,ISNULL(Allmonths, value)
ORDER BY 
    1, 3, 4

Answer 2

有2个逻辑，

i) 当 allmonths 为空时 ii) allmonths 不为空

首先以您想要的任何方式创建数字表，

Create Table tblNumber(Number int primary key)

INSERT INTO tblNumber
SELECT TOP 100000 ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) AS [N]
FROM dbo.syscolumns tb1,dbo.syscolumns tb2

最终脚本，

   select *
,ROW_NUMBER()over( partition by employeeid order by companyid)rn1
into #table1
from table1

;with CTE as
(
select T1.*
,ROW_NUMBER()over(partition by rn1,employeeid order by companyid)rn
,ROW_NUMBER()over(partition by employeeid order by companyid)rn2
,DATEDIFF(month,startdate,enddate)+1monthDiff from #table1 T1
inner join [dbo].[tblNumber1] n on n.number<=(DATEDIFF(month,startdate,enddate)+1)
)
,CTE2 as
(
select T1.*
,dateadd(month,(rn-1),t1.startdate)NewEndDate
from CTE T1

)
,CTE1 as
(
select t1.companyid,t1.employeeid,t1.startdate,dateadd(month,(rn-1),t1.startdate)NewEndDate
,t1.Enddate,rn,rn1
,t2.[value] as Final 
from CTE2 t1
cross apply(select top 1 [value] from table2 t2 where t2.employeeid=t1.employeeid 
and t2.companyid=t1.companyid and month=month(NewEndDate) and allmonths is null)t2
union all
select t1.companyid,t1.employeeid,t1.startdate,dateadd(month,(rn-1),t1.startdate)NewEndDate
,t1.Enddate,rn,rn1
,t2.[allmonths] as Final 
from CTE2 t1
cross apply(select top 1 allmonths from table2 t2 where t2.employeeid=t1.employeeid 
and t2.companyid=t1.companyid  and allmonths is not null)t2

)


select * from
(
select companyid, employeeid,min(NewEndDate)StartDate,eomonth(max(NewEndDate)) EndDate,Final
from CTE1
group by companyid, employeeid,Final,rn1
union all

select t1.companyid,t1.employeeid,t1.startdate,EndDate
,null as Final 
from #table1 t1
where not exists(select 1 from table2 t2 where t2.employeeid=t1.employeeid 
and t2.companyid=t1.companyid  )

)t4
order by employeeid,StartDate

drop table #table1

注意事项

i）我几个小时前采集了样本数据。

ii) 使用其他样本数据进行测试，如果它不适用于其他样本数据，则单独粘贴该样本数据。

iii）两个表都涉及多少行？

iv) 首先让输出得到纠正，然后可以优化查询。

v) 使用各种样本数据进行“allmonths 为空”时的第一次测试

vi) 然后用各种样本数据测试“allmonths is not null”