SET sql_mode=ORACLE;

delimiter |;
--error ER_INVALID_AGGREGATE_FUNCTION
create aggregate function f1(x INT) return INT AS
begin
  insert into t1(sal) values (x);
  return x;
end|

--error ER_NOT_AGGREGATE_FUNCTION
create function f1(x INT) return INT AS
begin
  set x=5;
  fetch group next row;
return x+1;
end |

DELIMITER ;|


CREATE TABLE marks(stud_id INT, grade_count INT); 
INSERT INTO marks VALUES (1,6), (2,4), (3,7), (4,5), (5,8);
SELECT * FROM marks;

--echo # Using PL/SQL syntax: EXCEPTION WHEN NO_DATA_FOUND

DELIMITER //;
CREATE AGGREGATE FUNCTION IF NOT EXISTS aggregate_count(x INT) RETURN INT AS
  count_students INT DEFAULT 0;
BEGIN  
  LOOP  
    FETCH GROUP NEXT ROW;  
    IF x THEN  
      count_students:= count_students + 1;
    END IF;  
  END LOOP;  
EXCEPTION
  WHEN NO_DATA_FOUND THEN
    RETURN count_students;
END aggregate_count //
DELIMITER ;//
SELECT aggregate_count(stud_id) FROM marks;
DROP FUNCTION IF EXISTS aggregate_count;


--echo # Using SQL/PSM systax: CONTINUE HANDLER

DELIMITER //;
CREATE AGGREGATE FUNCTION IF NOT EXISTS aggregate_count(x INT) RETURN INT AS
  count_students INT DEFAULT 0;
  CONTINUE HANDLER FOR NOT FOUND RETURN count_students;
BEGIN  
  LOOP  
    FETCH GROUP NEXT ROW;  
    IF x THEN  
      SET count_students= count_students + 1;
    END IF;  
  END LOOP;  
END //
DELIMITER ;//
SELECT aggregate_count(stud_id) FROM marks;
DROP FUNCTION IF EXISTS aggregate_count;


DROP TABLE marks;