i have modifed my function, but i have problems with declare variables. I used postgres 8.4. Have someone an idea?

        CREATE OR REPLACE FUNCTION requestcounterid(_mindate timestamptz, _maxdate timestamptz) 
          RETURNS TABLE (kategorien text, requestcounter int) AS
        $func$  
        DECLARE
        _minid bigint; 
        _maxid bigint; 
        
        BEGIN 
        
    SELECT id  INTO _minid from tablename where starttime >= $1 ORDER BY starttime ASC LIMIT 1; 
    SELECT id  INTO _maxid from tablename  where starttime < $2 ORDER BY starttime DESC LIMIT 1; 
        
        SELECT CASE WHEN duration <= 10000000 THEN '00-01 sec'::text
                    WHEN duration <= 40000000 THEN '01-04 sec'
                    WHEN duration <= 100000000 THEN '04-10 sec' 
                    WHEN duration <= 300000000 THEN '10-30 sec' 
                    WHEN duration <= 600000000 THEN '30-60 sec' 
                    ELSE 'more than 60 sec' END  
             , count(*)::int                     
        FROM   tablename
        WHERE  id >= _minid and id <= _maxid
        GROUP  BY 1                              
        ORDER  BY 1; 
        
        END; 
        $func$ LANGUAGE plpgsql; 

Error: 

    ERROR:  query has no destination for result data
    HINT:  If you want to discard the results of a SELECT, use PERFORM instead.
    CONTEXT:  PL/pgSQL function "requestcounterid" line 12 at SQL statement