REVERSE('стол') = 'лотс' 

CREATE OR REPLACE FUNCTION TOOLS.RESERVE (STR_IN VARCHAR(2000))
  RETURNS VARCHAR(32000)
  LANGUAGE SQL
  BEGIN
        DECLARE i INTEGER;
        DECLARE j INTEGER;
        DECLARE STR_OUT VARCHAR(32000);
        
        SET STR_OUT = '';
        SET STR_IN = LTRIM(RTRIM(STR_IN));
        set i = length(STR_IN);
           WHILE i >= 1  DO
                 SET STR_OUT =  STR_OUT || SUBSTR(STR_IN,i,1);
                 SET i = i -1;
           END WHILE;
           RETURN STR_OUT;
  END