Type: String Being Recognized as Date

Without knowing how this field is defined in the lookml, it’s hard to say for sure, but it looks like ${downtime_start} is a date field, so you should be able to use it in a diff_seconds() funtion by using one of the timeframes on that field like this:

diff_seconds(${downtime_start_time}, ${some_other_date_time})

Note the above assumes that both downtime_start and some_other_date are both dimension groups in the lookml. Hope this helps 🙂

I believe it might be argument type suggestion for the particular function (or might not be), not very sure on it.

Can you please check if it still shows Type: String even without downtime_start as an argument?

And apart from that, the error message itself is pretty clear.

That’s interesting… 🤔

Can you please share definition of downtime_start?

Right, so the issue here is that in your first example you had a date group, without a timeframe specified, so it read it as a string, but Looker knows it’s a date so it was preventing you from casting to date again (which would be redundant). In this second example, you’re referring to a specific timeframe within the dimension group, which Looker can also tell is a date, and is preventing casting again.

You should be able to use both ${downtime_start_time} and ${api_dataset.timestamp_time} in a diff_seconds() function without issue.