Select rows until a total amount is met in a column (mysql) - mysql

Question

I have seen this issue in SF, but me being a noob I just can't get my fried brain around them. So please forgive me if this feels like repetition.
My Sample Table
--------------------------
ID | Supplier | QTY
--------------------------
1 1 2
2 1 2
3 2 5
4 3 2
5 1 3
6 2 4
I need to get the rows "UNTIL" the cumulative total for "QTY" is equal or greater than 5 in descending order for a particular supplier id.
In this example, for supplier 1, it will be rows with the ids of 5 and 2.
Id - unique primary key
Supplier - foreign key, there is another table for supplier info.
Qty - double

Answer 1

It ain't pretty, but I think this does it and maybe it can be the basis of something less cumbersome. Note that I use a "fake" INNER JOIN just to get some variable initialized for the first time--it serves no other role.
SELECT ID,
supplier,
qty,
cumulative_qty
FROM
(
SELECT
ID,
supplier,
qty,
-- next line keeps a running total quantity by supplier id
#cumulative_quantity := if (#sup <> supplier, qty, #cumulative_quantity + qty) as cumulative_qty,
-- next is 0 for running total < 5 by supplier, 1 the first time >= 5, and ++ after
#reached_five := if (#cumulative_quantity < 5, 0, if (#sup <> supplier, 1, #reached_five + 1)) as reached_five,
-- next takes note of changes in supplier being processed
#sup := if(#sup <> supplier, supplier, #sup) as sup
FROM
(
--this subquery is key for getting things in supplier order, by descending id
SELECT *
FROM `sample_table`
ORDER BY supplier, ID DESC
) reverse_order_by_id
INNER JOIN
(
-- initialize the variables used to their first ever values
SELECT #cumulative_quantity := 0, #sup := 0, #reached_five := 0
) only_here_to_initialize_variables
) t_alias
where reached_five <= 1 -- only get things up through the time we first get to 5 or above.

Answer 2

How about this? Using two variables.
SQLFIDDLE DEMO
Query:
set #tot:=0;
set #sup:=0;
select x.id, x.supplier, x.ctot
from (
select id, supplier, qty,
#tot:= (case when #sup = supplier then
#tot + qty else qty end) as ctot,
#sup:=supplier
from demo
order by supplier asc, id desc) x
where x.ctot >=5
;
| ID | SUPPLIER | CTOT |
------------------------
| 2 | 1 | 5 |
| 1 | 1 | 7 |
| 3 | 2 | 5 |

Answer 3

Standard SQL has no concept of 'what row number am I up to', so this can only be implemented using something called a cursor. Writing code with cursors is something like writing code with for loops in other languages.
An example of how to use cursors is here:
http://dev.mysql.com/doc/refman/5.0/en/cursors.html

Answer 4

Here is a rough demo about cursor, may be it's helpful.
CREATE TABLE #t
(
ID INT IDENTITY,
Supplier INT,
QTY INT
);
TRUNCATE TABLE #t;
INSERT INTO #t (Supplier, QTY)
VALUES (1, 2),
(1, 2),
(2, 5),
(3, 2),
(1, 3);
DECLARE #sum AS INT;
DECLARE #qty AS INT;
DECLARE #totalRows AS INT;
DECLARE curSelectQTY CURSOR
FOR SELECT QTY
FROM #t
ORDER BY QTY DESC;
OPEN curSelectQTY;
SET #sum = 0;
SET #totalRows = 0;
FETCH NEXT FROM curSelectQTY INTO #qty;
WHILE ##FETCH_STATUS = 0
BEGIN
SET #sum = #sum + #qty;
SET #totalRows = #totalRows + 1;
IF #sum >= 5
BREAK;
END
SELECT TOP (#totalRows) *
FROM #t
ORDER BY QTY DESC;
CLOSE curSelectQTY;
DEALLOCATE curSelectQTY;

Answer 5

SELECT x.*
FROM supplier_stock x
JOIN supplier_stock y
ON y.supplier = x.supplier
AND y.id >= x.id
GROUP
BY supplier
, id
HAVING SUM(y.qty) <=5;