accumulated sum in query

Question

How is it possible to return rows with an accumulate sum for a row bigger or smaller than a specified value?

table:

id | count
-----------
1 | 30
2 | 10
3 | 5
4 | 20
5 | 15

query:

SELECT id, count
FROM table
ORDER BY id
HAVING SUM(count) < 50

return rows:

id | count
-------------
1 | 30
2 | 10
3 | 5

update

code:

public function query(){
    switch($this->table){
        case 'in_stock':
            return "SELECT * FROM ".Init::$static['db'].".stock
                WHERE id<=dynaccount.stock_first_available_id(".$this->value['num_stock'].", ".$this->value['product_id'].", ".(isset($this->att_arr['gid']) ? $this->att_arr['gid']:$_SESSION['gid']).")
                ORDER BY time, id";
    }
}

procedure:

DELIMITER $$

DROP FUNCTION IF EXISTS `stock_first_available_id` $$
CREATE DEFINER=`dynaccount`@`localhost` FUNCTION `stock_first_available_id`(_running_total_limit INT, _product_id INT, _group_id INT) RETURNS INT
BEGIN
    DECLARE _running_count INT default 0;
    DECLARE _id INT;
    DECLARE _current_id INT;
    DECLARE _sum_count INT;

    IF (SELECT COUNT(*) FROM stock WHERE group_id=_group_id && type=2 && product_id=_product_id) = 0 THEN
        RETURN 0;
    END IF;

    DECLARE _cur CURSOR FOR SELECT id, count FROM stock WHERE group_id=_group_id && type=2 && product_id=_product_id ORDER BY time DESC, id DESC;

    OPEN _cur;

    read_loop: LOOP
        FETCH _cur INTO _id, _sum_count;

        SET _running_count = _running_count + _sum_count;
        SET _current_id = _id;

        IF _running_count > _running_total_limit THEN
            LEAVE read_loop;
        END IF;
    END LOOP read_loop;

    CLOSE _cur;

    RETURN _current_id;
END $$

DELIMITER ;

error:

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DECLARE _cur CURSOR FOR SELECT id, count FROM stock WHERE group_id=_group_id && ' at line 12 

Answer 1

The following query:

SELECT * FROM 
(SELECT id, 
       count, 
       @running_count := @running_count + count AS Counter 
  FROM sumtest, (SELECT @running_count := 0) AS T1 ORDER BY id) AS TableCount 

WHERE TableCount.Counter < 50;

produces the results:

id  count   Counter
1   30      30
2   10      40
3   5       45

I copied your table into MySql and called it "sumtest" btw. Please replace with your table name.

Effectively, we work out the running total, in id order, then use that as a subquery.

So this query:

SELECT id, 
       count, 
       @running_count := @running_count + count AS Counter 
FROM sumtest, (SELECT @running_count := 0) AS T1 
ORDER BY id

Produces:

id  count   Counter
1   30      30
2   10      40
3   5       45
4   20      65
5   15      80

So then it becomes a trivial matter to select all those rows where the counter is less than your desired sum by performing another select on this.

EDIT: Here is an example with a cursor. I've just thrown this function together for you (note my table is called sumtest and my account is the default root@localhost):

DELIMITER $$

DROP FUNCTION IF EXISTS `Test_Cursing` $$
CREATE DEFINER=`root`@`localhost` FUNCTION `Test_Cursing`(_running_total_limit INT) RETURNS int
BEGIN
  /* Why am I on StackOverflow at 01:41 on New Years Day. Dear oh dear, where's the beer? */
  DECLARE _running_count INT default 0;
  DECLARE _id INT;
  DECLARE _current_id INT;
  DECLARE _sum_count INT;

  DECLARE _cur CURSOR FOR SELECT id, count FROM sumtest ORDER BY id;

  OPEN _cur;

  read_loop: LOOP
    FETCH _cur INTO _id, _sum_count;

    SET _running_count = _running_count + _sum_count;

    IF _running_count > _running_total_limit   THEN
      LEAVE read_loop;
    END IF;

    SET _current_id = _id;

  END LOOP;

  CLOSE _cur;

    RETURN _current_id;

END $$

DELIMITER ;

Calling it this way:

SELECT Test_Cursing(50);

will return id = 3 - that is, the last id before the running total limit is breached. You can then use this to:

 SELECT * FROM sumtest WHERE id <= Test_Cursing(50);

Which returns:

id  count
1   30
2   10
3   5