CREATE OR REPLACE FUNCTION myfunction(integer) 
RETURNS integer AS '
  DECLARE
   nm ALIAS FOR $1;
    cub INTEGER;
  BEGIN
   cub:=nm;
    WHILE cub <=3 LOOP
      cub := cub * cub * cub;
    END LOOP;
    RETURN cub;
  END;
' LANGUAGE 'plpgsql';

SELECT myfunction(2);

-- 10. Cykly, FOR
 [ <<label>> ]
  FOR identifier IN [ REVERSE ] expression1 .. expression2  LOOP
      statement;
      [...]
  END LOOP;
  
  CREATE OR REPLACE FUNCTION myfunction(dt DATE) 
RETURNS INTEGER 
AS 
$$ 
DECLARE ddt DATE; 
        num  INTEGER; 
        x  INTEGER; 
BEGIN 
   ddT := dt; 
   x := EXTRACT(MONTH FROM dt); 
   FOR i IN 1 .. 31 
   LOOP  
      num := i;          
      EXIT WHEN EXTRACT(MONTH FROM ddt + i * INTERVAL '1 DAY') <> x; 
   END LOOP; 
   RETURN num-1;    
END; 
$$ 
LANGUAGE PLPGSQL;

SELECT myfunction(CURRENT_DATE);