Create date custom field

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1

I have a table that has 3 silly columns, they are day, month and year.
I want to join these to create a date column, I used Custom expression with concat however it comes out as text which I can expect, but how do I make it a date field.
Was thinking about using data model but not sure where to begin.
any help will be appreciated

thanks

2

We don’t yet cast fields in custom columns, you should be building this either in a Metabase model via sql or in a database view