Question

I have a database with two tables. The first (‘calendar’) contains only a series of dates like ‘2012-12-25’ into the future. This was generated by a procedure. The second (‘new_allocations’) contains a series of stock allocations. Sample content looks like this:

+----+-------------+------------+----------+------------+
| id | delivery_ID | date       | quantity | product_ID |
+----+-------------+------------+----------+------------+
|  1 |           1 | 2012-11-09 |        5 |          2 |
|  2 |           1 | 2012-11-08 |        5 |          2 |
|  3 |           2 | 2012-11-07 |        5 |          2 |
|  4 |           3 | 2012-11-06 |        5 |          2 |
|  5 |           4 | 2012-11-03 |        2 |          2 |
|  6 |           4 | 2012-11-02 |        5 |          2 |
|  7 |           5 | 2012-11-03 |        3 |          2 |
|  8 |           6 | 2012-11-05 |        5 |          2 |
|  9 |           7 | 2012-11-07 |       55 |          5 |
| 10 |           7 | 2012-11-06 |       34 |          5 |
| 11 |           7 | 2012-11-05 |       40 |          5 |
+----+-------------+------------+----------+------------+

The following query (which basically means ‘show me a list of days in the date range supplied, excluding Sundays, with a total of stock allocations for that day’) is almost what I want, except that it is for all products (denoted by ‘product_ID’).

select datefield as Date, sum(ifnull(quantity,0)) as Qty from calendar left join new_allocations on (new_allocations.date=calendar.datefield) where (calendar.datefield>='2012-10-29' and calendar.datefield<='2012-11-10') and dayname(calendar.datefield) != 'Sunday' group by datefield;

+------------+------+
| Date       | Qty  |
+------------+------+
| 2012-10-29 |    0 |
| 2012-10-30 |    0 |
| 2012-10-31 |    0 |
| 2012-11-01 |    0 |
| 2012-11-02 |    5 |
| 2012-11-03 |    5 |
| 2012-11-05 |   45 |
| 2012-11-06 |   39 |
| 2012-11-07 |   60 |
| 2012-11-08 |    5 |
| 2012-11-09 |    5 |
| 2012-11-10 |    0 |
+------------+------+

So my problem is that as soon as I add “and product_ID=’2′” the query stops returning all dates in the range:

New query:

select datefield as Date, sum(ifnull(quantity,0)) as Qty from calendar left join new_allocations on (new_allocations.date=calendar.datefield) where (calendar.datefield>='2012-10-29' and calendar.datefield<='2012-11-10') and dayname(calendar.datefield) != 'Sunday' and product_ID='2' group by datefield;

New result:

+------------+------+
| Date       | Qty  |
+------------+------+
| 2012-11-02 |    5 |
| 2012-11-03 |    5 |
| 2012-11-05 |    5 |
| 2012-11-06 |    5 |
| 2012-11-07 |    5 |
| 2012-11-08 |    5 |
| 2012-11-09 |    5 |
+------------+------+

In fact what I want looks like this:

+------------+------+
| Date       | Qty  |
+------------+------+
| 2012-10-29 |    0 |
| 2012-10-30 |    0 |
| 2012-10-31 |    0 |
| 2012-11-01 |    0 |
| 2012-11-02 |    5 |
| 2012-11-03 |    5 |
| 2012-11-05 |    5 |
| 2012-11-06 |    5 |
| 2012-11-07 |    5 |
| 2012-11-08 |    5 |
| 2012-11-09 |    5 |
| 2012-11-10 |    0 |
+------------+------+

I have been backwards and forwards through this and have not been able to phrase the query correctly – what am I missing?

Many thanks in advance.

CREATE TABLE `new_allocations` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `delivery_ID` int(11) DEFAULT NULL,
  `date` date DEFAULT NULL,
  `quantity` int(11) DEFAULT NULL,
  `product_ID` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
)

INSERT INTO `new_allocations` (`id`, `delivery_ID`, `date`, `quantity`, `product_ID`)
VALUES
    (1,1,'2012-11-09',5,2),
    (2,1,'2012-11-08',5,2),
    (3,2,'2012-11-07',5,2),
    (4,3,'2012-11-06',5,2),
    (5,4,'2012-11-03',2,2),
    (6,4,'2012-11-02',5,2),
    (7,5,'2012-11-03',3,2),
    (8,6,'2012-11-05',5,2),
    (9,7,'2012-11-07',55,5),
    (10,7,'2012-11-06',34,5),
    (11,7,'2012-11-05',40,5);

For the calendar:

DROP TABLE IF EXISTS `calendar`;
CREATE TABLE `calendar` (
  `datefield` date DEFAULT NULL
)

The procedure to fill the calendar:

DELIMITER ;;
CREATE DEFINER=`root`@`localhost` PROCEDURE `fill_calendar`(start_date DATE, end_date DATE)
BEGIN
  DECLARE crt_date DATE;
  SET crt_date=start_date;
  WHILE crt_date < end_date DO
    INSERT INTO calendar VALUES(crt_date);
    SET crt_date = ADDDATE(crt_date, INTERVAL 1 DAY);
  END WHILE;
END;;
DELIMITER ;

Answer 1

Add your condition into the ON clause, not the WHERE clause:

SELECT  datefield AS Date, COALESCE(SUM(quantity), 0) AS Qty
FROM    calendar
LEFT JOIN
        new_allocations
ON      new_allocations.date = calendar.datefield
        AND product_ID = '2'
WHERE   calendar.datefield BETWEEN '2012-10-29' AND '2012-11-10'
        AND dayname(calendar.datefield) != 'Sunday'
GROUP BY
        datefield

WHERE filters the results of the join. If there were no allocations for a given date, the left join will yield one record for the date with all new_allocations fields (including productId) set to NULL.