SQL case nesting

/*************************************** **************************************** ******************************/
-- Calculate the overtime hours for non-fixed employees
/*************************************** **************************************** ******************************/
Create proc recountworkhourfordf
@ Begindate varchar (10 ),
@ Enddate varchar (10)
As
------------- Delete the overtime record on the Operation Date ------------------------------------------------
Delete from workhourdetail
Where (carddate between @ begindate and @ enddate)
And (left (CDAY, 1) = 'D' or left (CDAY, 1) = 'F ')

Insert into workhourdetail (ecode, carddate, CDAY, factworkhour)
Select -- A. ecode, A. ename, A. card1, A. card2, A. addtime, B. btime, B. etime, CDAY, A. carddate,
A. ecode, A. carddate, B. CDAY,
Case when substring (CDAY, 2, 1) = '*' then
---------------------------- Call the work card before normal work --------------------------------------
Case when (card1 <= B. btime and card1> '12: 00') then
Case when (card2 <B. setime and card2> '12: 00') then
Case when (datediff (MI, B. btime, card2) % 60)> = 30 then
Cast (datediff (MI, B. btime, card2)/60) as varchar (2) + '. 5'
Else
Cast (datediff (MI, B. btime, card2)/60) as varchar (2) + '. 0'
End
When (card2> = B. setime) and (card2 <'24: 00') and (left (CDAY, 1) = 'F') then
'4. 0'
When (card2> = B. xbtime) and (card2 <B. etime) then
Case when (datediff (MI, B. xbtime, card2) % 60)> = 30 then
Cast (datediff (MI, B. xbtime, card2) + 240)/60) as varchar (2) + '. 5'
Else
Cast (datediff (MI, B. xbtime, card2) + 240)/60) as varchar (2) + '. 0'
End
When (card2> = B. etime) and (card2 <= B. bworktime) then
'8. 0'
When (card2> B. bworktime and card2 <'12: 00') then
Case when (datediff (MI, B. bworktime, card2) % 60)> = 30 then
Cast (datediff (MI, B. bworktime, card2) + 480)/60) as varchar (2) + '. 5'
Else
Cast (datediff (MI, B. bworktime, card2) + 480)/60) as varchar (2) + '. 0'
End
Else
'0. 0'
End
--------------------------- Call the work card before the first half of the day ------------------------------------
When (card1> = B. btime) and (card1 <B. setime) then
Case when (card2 <B. setime and card2> '12: 00') then
Case when (datediff (MI, begincard, card2) % 60)> = 30 then
Cast (datediff (MI, begincard, card2)/60) as varchar (2) + '. 5'
Else
Cast (datediff (MI, begincard, card2)/60) as varchar (2) + '. 0'
End
When (card2> = B. setime) and (card2 <'24: 00') then
Case when (datediff (MI, begincard, B. setime) % 60)> = 30 then
Cast (datediff (MI, begincard, B. setime)/60) as varchar (2) + '. 5'
Else
Cast (datediff (MI, begincard, B. setime)/60) as varchar (2) + '. 0'
End
When (card2> B. xbtime) and (card2 <B. etime) and (card2 <'12: 00') then
Case when (datediff (MI, begincard, B. setime) + datediff (MI, B. xbtime, card2) % 60)> = 30 then
Cast (datediff (MI, begincard, B. setime) + datediff (MI, B. xbtime, card2)/60) as varchar (2) + '. 5'
Else
Cast (datediff (MI, begincard, B. setime) + datediff (MI, B. xbtime, card2)/60) as varchar (2) + '. 0'
End
When (card2> = B. etime) and (card2 <= B. bworktime) then
Case when (datediff (MI, begincard, B. setime) + 240) % 60)> = 30 then
Cast (datediff (MI, begincard, B. setime) + 240)/60) as varchar (2) + '. 5'
Else
Cast (datediff (MI, begincard, B. setime) + 240)/60) as varchar (2) + '. 0'
End
When (card2> B. bworktime and card2 <'12: 00') then
Case when (datediff (MI, begincard, B. setime) + 240 + datediff (MI, B. bworktime, card2) % 60)> = 30 then
Cast (datediff (MI, begincard, B. setime) + 240 + datediff (MI, B. bworktime, card2)/60) as varchar (2) + '. 5'
Else
Cast (datediff (MI, begincard, B. setime) + 240 + datediff (MI, B. bworktime, card2)/60) as varchar (2) + '. 0'
End
Else
'0. 0'
End
--------------------------- Call the work card before the next half day before work ------------------------------------
When (card1> = B. setime and card1> '12: 00') then
Case when (card2> B. xbtime) and (card2 <B. etime) then
Case when (datediff (MI, B. xbtime, card2) % 60)> = 30 then
Cast (datediff (MI, B. xbtime, card2)/60) as varchar (2) + '. 5'
Else
Cast (datediff (MI, B. xbtime, card2)/60) as varchar (2) + '. 0'
End
When (card2> = B. etime) and (card2 <= B. bworktime) then
'4. 0'
When (card2> B. bworktime and card2 <'12: 00') then
Case when (240 + datediff (MI, B. bworktime, card2) % 60)> = 30 then
Cast (240 + datediff (MI, B. bworktime, card2)/60) as varchar (2) + '. 5'
Else
Cast (240 + datediff (MI, B. bworktime, card2)/60) as varchar (2) + '. 0'
End
Else
'0. 0'
End
--------------------------- Get off work card before the next half day ------------------------------------
When (card1> = B. xbtime and card1 <B. etime and card1 <'12: 00') then
Case when (card2 <B. etime) then
Case when (datediff (MI, begincard, card2) % 60)> = 30 then
Cast (datediff (MI, begincard, card2)/60) as varchar (2) + '. 5'
Else
Cast (datediff (MI, begincard, card2)/60) as varchar (2) + '. 0'
End
When (card2> = B. etime) and (card2 <= B. bworktime) then
Case when (datediff (MI, begincard, B. etime) % 60)> = 30 then
Cast (datediff (MI, begincard, B. etime)/60) as varchar (2) + '. 5'
Else
Cast (datediff (MI, begincard, B. etime)/60) as varchar (2) + '. 0'
End
When (card2> B. bworktime and card2 <'12: 00') then
Case when (datediff (MI, begincard, card2)-datediff (MI, B. etime, B. bworktime) % 60)> = 30 then
Cast (datediff (MI, begincard, card2)-datediff (MI, B. etime, B. bworktime)/60) as varchar (2) + '. 5'
Else
Cast (datediff (MI, begincard, card2)-datediff (MI, B. etime, B. bworktime)/60) as varchar (2) + '. 0'
End
Else
'0. 0'
End
When (card1> = B. etime and card1 <= B. bworktime) then
Case when (card2> B. bworktime) then
Case when (datediff (MI, B. bworktime, card2) % 60)> = 30 then
Cast (datediff (MI, B. bworktime, card2)/60) as varchar (2) + '. 5'
Else
Cast (datediff (MI, B. bworktime, card2)/60) as varchar (2) + '. 0'
End
Else
'0. 0'
End
When (card1> B. bworktime) then
Case when (card2> card1 and card2> B. bworktime) then
Case when (datediff (MI, begincard, card2) % 60)> = 30 then
Cast (datediff (MI, begincard, card2)/60) as varchar (2) + '. 5'
Else
Cast (datediff (MI, begincard, card2)/60) as varchar (2) + '. 0'
End
Else
'0. 0'
End

Else
'0. 0'
End
Else
Case when (datediff (MI, B. bworktime, card2)> = 30) and card2 <= '12: 00') then
Case when (datediff (MI, B. bworktime, card2) % 60)> = 30 then
Cast (datediff (MI, B. bworktime, card2)/60) as varchar (2) + '. 5'
Else
Cast (datediff (MI, B. bworktime, card2)/60) as varchar (2) + '. 0'
End
Else
'0. 0'
End
End factworkhour
From cardrecord A, empclass B
Where a. ecode = B. workid and A. carddate = B. prodate -- and A. ecode in (select ecode from emploees where emoneyfix = 0)
And (A. carddate between @ begindate and @ enddate)
And (left (CDAY, 1) = 'D' or left (CDAY, 1) = 'F ')
-- And A. carddate in ('2017-12-01 ', '2017-12-02', '2017-12-06 ', '2017-12-08', '2017-12-09 ')

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