Get work time in minutes based on shift schedule - sql

Question

In production we have 3 shifts. Each Shift timing is described in table tbl_ShiftSched:
WT - work time, PT - break time.
ShiftTmID - schedule for 2 and for 3 shifts.
I am looking for easy way to get work time in minutes having start and end time.
For example, having input between #2015.05.29 06:10:00# and #2015.05.29 09:30:00# and tbl_WorkStations.WksID='GRD' (Workstation code with relation on ShiftTmID ='3P') should give output 190 min.
I have function in MS Access which gives me needed output. But when migrated to T-SQL it becomes very complicated because I do not find easy way how to use alias in T-SQL. Here is the code:
USE [STRDAT]
GO
declare
#strWks varchar(3),
#dteIN datetime='2013.08.05 03:30',
#dteOUT datetime='2013.08.05 05:30',
#strShf varchar(12)=null,--'2013.08.04-3',
#strInd varchar(2) = 'WT',
#dteFTm datetime,
#dteShf date
--#PrdS datetime,
--#PrdE datetime
select top 1
#dteFTm =
case
when #strShf is not null
then (select shiftstart from tbl_ShiftSched where ShiftTmID=(select ShiftTiming from tbl_WorkStations where WksID=#strWks) and shift=right(#strshf,1) and sortind=1)
else #dteIN-dateadd(day,datediff(day,0,#dteIN),0) --CAST(#dteIN-cast(floor(#dteIN) as float) as datetime)
end,
#dteShf=
case
when #strShf is not null
then left(#strShf,10)
else convert(varchar,dateadd(day,datediff(day,0,#dteIN),0),102)
end
--select #dteftm,#dteShf
SELECT tbl_ShiftSched.Shift,
tbl_ShiftSched.SortInd,
[ShiftStart]+
case
when #dteFTm>[shiftstart]
then DateAdd(day,1,#dteShf)
else #dteShf
end AS PrdS,
[ShiftEnd]+
case
when #dteFTm>[shiftend]
then DateAdd(day,1,#dteShf)
else #dteShf
end AS PrdE,
case
when #dteIN>=[PrdS] AND [PrdE]>=#dteOUT
then DateDiff(minute,#dteIN,#dteOUT)
else case
when #dteIN<=[PrdS] AND [PrdE]<=#dteOUT
then DateDiff(minute,[PrdS],[PrdE])
else case
when [PrdS]<=#dteIN AND #dteIN<=[PrdE]
then DateDiff(minute,#dteIN,[Prde])
else case
when [PrdS]<=#dteOUT AND #dteOUT<=[PrdE]
then DateDiff(minute,[Prds],#dteOUT)
else 0
end
end
end
end AS Tm,
#dteIN AS S,
#dteOUT AS E,
tbl_ShiftSched.ShiftType,tbl_ShiftSched.ShiftStart,tbl_ShiftSched.ShiftEnd
FROM tbl_WorkStations
INNER JOIN tbl_ShiftSched ON tbl_WorkStations.ShiftTiming = tbl_ShiftSched.ShiftTmID
WHERE (((tbl_WorkStations.WksID)=#strWks))
Off course it gives me an error Invalid column name 'PrdS' and 'PrdE' because I use alias.
Must be some more easy way to achieve it. Maybe I am on wrong direction?...

Answer 1

Whenever I have to calculate a field and use the results in a second field, I use a common table expression to make the first calculation. Given this query, it could look like this:
with cte_preprocess as
(
SELECT tbl_ShiftSched.Shift,
tbl_ShiftSched.SortInd,
[ShiftStart]+
case
when #dteFTm>[shiftstart]
then DateAdd(day,1,#dteShf)
else #dteShf
end AS PrdS,
[ShiftEnd]+
case
when #dteFTm>[shiftend]
then DateAdd(day,1,#dteShf)
else #dteShf
end AS PrdE,
tbl_ShiftSched.ShiftType,tbl_ShiftSched.ShiftStart,tbl_ShiftSched.ShiftEnd
FROM tbl_WorkStations
INNER JOIN tbl_ShiftSched ON tbl_WorkStations.ShiftTiming = tbl_ShiftSched.ShiftTmID
WHERE (((tbl_WorkStations.WksID)=#strWks))
)
SELECT [Shift]
, SortInd
, PrdS
, PrdE
, case
when #dteIN>=[PrdS] AND [PrdE]>=#dteOUT
then DateDiff(minute,#dteIN,#dteOUT)
else case
when #dteIN<=[PrdS] AND [PrdE]<=#dteOUT
then DateDiff(minute,[PrdS],[PrdE])
else case
when [PrdS]<=#dteIN AND #dteIN<=[PrdE]
then DateDiff(minute,#dteIN,[Prde])
else case
when [PrdS]<=#dteOUT AND #dteOUT<=[PrdE]
then DateDiff(minute,[Prds],#dteOUT)
else 0
end
end
end
end AS Tm
, #dteIN
, #dteOUT
, ShiftEnd
FROM cte_preprocess
More on CTE's here