I can't find a solution for this problem after a couple of hours of research. The query is:
SELECT searchaddress('some string'); FETCH ALL IN mycursor;
The function searchaddress returns a REFCURSOR, named mycursor. In PostgreSQL using FETCH I get results. Using the exact same query (no parameters) in a Geoserver SQL View I get an error:
ERROR: syntax error at or near ";" Position: 73
If you need more information I will provide.
Edit: One more piece of information. The query used to be:
SELECT searchaddress('some string'); FETCH ALL IN "<unnamed cursor 1>";
Under this format it was anyone's guess what was the number of "unnamed cursor i". But the SQL View did return a response and not an error when I managed to guess the number of the cursor. Because I don't know how to guess the number I had the function searchaddress changed so it would return a cursor named "mycursor". At that point the querry stoped working altogether under Geosever.