There are quite few articles and blog posts on the subject, suggest you start with this one.
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Sometimes I really wonder.... can one possibly help?
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And why is this not a surprise :crazy:

What you have here is a classical example of a multi statement table valued function, absolute horror when it comes to performance!
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The good news is that...

Don't use RAID5, outdated and cannot handle the current volume sizes, unless you are willing to risk your data!
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Quick thoughts
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1) How different are the roles of a BI Developer and a Data Analyst? When I do Power BI I do a good level of...

For fun, here is a function that calculates the number of days in a year (leap year or normal year)
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USE TEEST;
GO

My thought is that using substring to grab the relevant bytes is more appropriate than implicitly doing so via convert.
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Thanks for the question Steve.

Here...

Can you post the expected results please?
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In the meantime, this might help

USE TEEST;
GO
SET NOCOUNT ON;

IF OBJECT_ID(N'dbo.TBL_EMP022')...

You are over-complicating this since you already have the calculations in the calendar table.
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This should help you out.

USE TEEST;
GO
SET...