SQL function parameter does not work

[BBergerac]

I have created this SQL function in Studio (on FUNCTIONS page):

select from person where firstName = qfirstName

qfirstName is the parameter
Executing returns no result.

Using a fixed string works, e.g.
select from person where firstName = "Gabi"
Is this a bug or do I make something wrong?

The documentationm only includes examples for JS but I prefer SQL. And the examples don't work qand I don't know how to enable the access to classes or packages in my JS code (but this is another issue).