Calculate the Days Between First and Last Orders

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  • Nice question to start the week on, thanks Kathi

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  • Ah well.

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  • Good one!

    Until I understood the framing context, I used to do the LAST_VALUE as FIRST_VALUE(.. ORDER BY [col] DESC), which works out the same, but is likely a worse approach from a query plan perspective. At least if you have indexes in place to support the ordering.

    Just because you're right doesn't mean everybody else is wrong.

  • Or you could do it totally old school by MIN(OrderDate), MAX(OrderDate) and GROUP BY CusomerID. And it would be faster, too.

    Is there any reason to overcomplicate things?

  • In this case, it would work. I should probably have pulled a different column like the amount. I wanted to show that you can use FIRST_VALUE and LAST_VALUE to pull values from the first and last rows. It's not always the same as MIN and MAX.

  • Yes, amount of first and last customer purchase would require a different solution. Sorry for my rant then.

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