Why am I not able to add a variable amount of time to a datetime column in a custom expression?

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1

Hey, new here. Not sure if this is a bug or if I'm misunderstanding how to do this. Either way, I couldn't find this in the GitHub issues.

I want to add a certain amount of time to a datetime column depending on a condition. In this example using the sample database, if the discount is below 3, then return 3, else 2.

I first define the condition using a custom column and case function. Then, I want to make another column using the function datetimeAdd(), and add a certain amount of days to the product -> created at column. For the amount of units to be added, I use the custom column. However, I get an invalid expression error. Upon checking the SQL I do see that the case function returns integers. Why can't the variable be used as an amount of time to be added?

Supplementary info:

Screenshot 2024-07-22 at 15.25.14
Screenshot 2024-07-22 at 15.25.142880×1500 367 KB

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2

Hey there!

In my opinion your issue is due to how SQL works.

You cannot use a custom column (Number of days to add) directly in another field within the same SELECT statement.

There are a few solutions:

  • Do not use the Question UI, but use directly SQL with a dedicated WITH statement.
  • Create an intermediate model in which you pre-define your CASE WHEN condition, and then build your additional logic on top of that model.

Hope this helps!

3

If you were writing SQL, you wouldn't be able to do that either.

Try something like this (sort out your own field names):

case (discount < 3 then datetimeadd(created, 3, "day),
datetimeadd(created, 2,"day"))
1 Like
4

Ah great, the solution above works. Thanks!