Issue while calculating SLA in SQL - sql

Question

I am using below function to calculate the elapsed time between 2 input timestamps. Only time spent during business hours should be calculated. Business hrs are Mon-Sat 8 am to 6 pm.
Function call syntax:
select xxxxx('2018.09.28 19:02:28','2018-09-29 10:40:35') Function is giving output as 98 mins, the correct answer is 160 mins.
Function structure is:
Create FUNCTION xxxxx (#LeadAssignTime DATETIME, #LeadContactTime DATETIME)
RETURNS VARCHAR(9)
AS
BEGIN
DECLARE #Temp BIGINT
SET #Temp=0
DECLARE #LeadAssignDay VARCHAR(9)
SET #LeadAssignDay = CONVERT(VARCHAR(9),#LeadAssignTime, 112)
DECLARE #LeadContactDay VARCHAR(9)
SET #LeadContactDay = CONVERT(VARCHAR(9),#LeadContactTime, 112)
DECLARE #StartTime VARCHAR(9)
SET #StartTime = CONVERT(VARCHAR(9),#LeadAssignTime, 108)
DECLARE #FinishTime VARCHAR(9)
SET #FinishTime = CONVERT(VARCHAR(9),#LeadContactTime, 108)
DECLARE #WorkStart VARCHAR(9)
SET #WorkStart = '08:00:00'
DECLARE #WorkFinish VARCHAR(9)
SET #WorkFinish = '18:00:00'
IF (#StartTime<#WorkStart)
BEGIN
SET #StartTime = #WorkStart
END
IF (#FinishTime>#WorkFinish)
BEGIN
SET #FinishTime=#WorkFinish
END
DECLARE #CurrentDate VARCHAR(9)
SET #CurrentDate = CONVERT(VARCHAR(9),#LeadAssignTime, 112)
DECLARE #LastDate VARCHAR(9)
SET #LastDate = CONVERT(VARCHAR(9),#LeadContactTime, 112)
WHILE(#CurrentDate<=#LastDate)
BEGIN
IF (DATEPART(dw, #CurrentDate)!=1 )
BEGIN
IF (#CurrentDate!=#LeadAssignDay) AND (#CurrentDate!=#LeadContactDay)
BEGIN
SET #Temp = (#Temp + (8*60))
END
ELSE IF (#CurrentDate=#LeadAssignDay) AND (#CurrentDate!=#LeadContactDay)
BEGIN
SET #Temp = #Temp + DATEDIFF(MINUTE, #StartTime, #WorkFinish)
END
ELSE IF (#CurrentDate!=#LeadAssignDay) AND (#CurrentDate=#LeadContactDay)
BEGIN
SET #Temp = #Temp + DATEDIFF(MINUTE, #WorkStart, #FinishTime)
END
ELSE IF (#CurrentDate=#LeadAssignDay) AND (#CurrentDate=#LeadContactDay)
BEGIN
SET #Temp = DATEDIFF(MINUTE, #StartTime, #FinishTime)
END
END
SET #CurrentDate = CONVERT(VARCHAR(9),DATEADD(day, 1, #CurrentDate),112)
END
Return #TEMP
END

Answer 1

You're going around your loop twice, but in the first iteration, you fall into the second IF block and setting #temp to be -62
In the second iteration, you fall into the third IF block and calculate 160 for the difference between #WorkStart and #FinishTime, but then this is added to the value already in #Temp. 160-62 = 98.
You'll need your second IF block to check if 'start time' is before 'work finish' before executing that logic.
(#CurrentDate=#LeadAssignDay) AND (#CurrentDate!=#LeadContactDay)
needs to become
(#CurrentDate=#LeadAssignDay) AND (#CurrentDate!=#LeadContactDay) AND ( #StartTime < #WorkFinish)
I haven't done any vetting beyond the one use case. Make sure to do some thorough testing.