How to make a function that will make a select with group by and join'om?

Question

SQL

Previously worked with MySQL and MsSQL. I want to make a function that will make a select with group by and join. The output is SETOF. And here is SETOF of what? I don't have such a table. VIew is not suitable, because parameters are passed to the function for filtering.

Answer 1

If I understand correctly, the solution is here.
info-comp.ru/obucheniest/197--sql-return-table.html
Adapt to your task