Filter on a field created by a Picklist

Filter on a field created by a Picklist

Ok, I'm confused about how this works . . . .
I'm trying to filter data like this -

if ((count(Workshop_Job[Assignee == input.Owner])  >  0)  ||  (input.Owner  ==  "-Select-"))

But I want to also filter by a field from Workshop_Job that is derived from a Picklist - a 'Status' field.
But the field 'Status' supposedly doesn't exist in Workshop_Job.
This is evidently because it is derived from a Picklist.
I don't get it. 
So how can I filter the Workshop_Job records by 'Assignee' AND 'Status' like -


if ((count(Workshop_Job[Assignee == input.Owner && Status == input.Status])  >  0 ) ||  (input.Owner  ==  "-Select-"))

Appreciate the help!

Cheers - Graeme