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 Please help explain how this SQL code works :-)

Author  Topic 

Maverick_
Posting Yak Master

107 Posts

Posted - 2014-01-07 : 06:01:32
Hi guys,

I have an SQL code below which removes weekends and non working days when calculating days difference between two dates:

ce.enquiry_time represents when the enquiry was logged

(DATEDIFF(dd, ce.enquiry_time, getdate()) + 1)
-(DATEDIFF(wk, ce.enquiry_time, getdate()) * 2)

-(CASE WHEN DATENAME(dw, ce.enquiry_time) = 'Sunday' THEN 1 ELSE 0 END)
-(CASE WHEN DATENAME(dw, getdate()) = 'Saturday' THEN 1 ELSE 0 END)

-(SELECT COUNT(*) FROM nonworking_day WHERE nonworking_day.nonworking_date >= ce.enquiry_time AND nonworking_day.nonworking_date < dateadd(dd,datediff(dd,0,getdate()),1))

It works but I don't understand how it works it out. I am having issues understanding each coloured piece of code and how it works together.

Any kind soul care to help break it down please

visakh16
Very Important crosS Applying yaK Herder

52326 Posts

Posted - 2014-01-07 : 06:31:42
(DATEDIFF(dd, ce.enquiry_time, getdate()) + 1) -> this gives total no of days between current date and ce.enquiry_time value

(DATEDIFF(wk, ce.enquiry_time, getdate()) * 2) -> this is to subtract the number of weekend days that happens between current date and ce.enquiry_time. there are 2 days per week so (no of weeks ) * 2 will give totals weekend days excluding starting and ending dates


(CASE WHEN DATENAME(dw, ce.enquiry_time) = 'Sunday' THEN 1 ELSE 0 END) -> checking if starting date is weekend day to subtract it too from total

(CASE WHEN DATENAME(dw, getdate()) = 'Saturday' THEN 1 ELSE 0 END) -> checking if ending date is weekend day to subtract it too from total

(SELECT COUNT(*) FROM nonworking_day WHERE nonworking_day.nonworking_date >= ce.enquiry_time AND nonworking_day.nonworking_date < dateadd(dd,datediff(dd,0,getdate()),1)) -> this will subtract any other holidays excluding weekends by looking at a table storing holiday details that falls between start and end dates.


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