Complex MySQL query between two tables - mysql

Question

I've a real complex query here, at least for me.
Here's a table with car dates releases (where model_key = 320D):
+------------+-----------+
| date_key | model_key |
+------------+-----------+
| 2003-08-13 | 320D |
| 2005-11-12 | 320D |
| 2007-02-11 | 320D |
+------------+----------+
Then I have a table with daily purchases (where model_key = 320D):
+------------+-----------+-----------+
| date_key | model_key | sal_quant |
+------------+-----------+ ----------+
| 2003-08-13 | 320D | 0 |
| 2003-08-14 | 320D | 1 |
| 2003-08-15 | 320D | 2 |
| 2003-08-16 | 320D | 0 |
...
| 2005-11-12 | 320D | 2 |
| 2005-11-13 | 320D | 0 |
| 2005-11-14 | 320D | 4 |
| 2005-11-15 | 320D | 3 |
...
| 2007-02-11 | 320D | 1 |
| 2007-02-12 | 320D | 0 |
| 2007-02-13 | 320D | 0 |
| 2007-02-14 | 320D | 0 |
...
+------------+-----------+-----------|
I want to know the sum of car sales by day after each release during N days.
I want a table like (assuming 4 days analysis):
+-----------------+
| sum(sal_quant) |
+-----------------+
| 3 |
| 1 |
| 6 |
| 3 |
+-----------------+
Which means, in the first day of car release, 3 BMW 320D were sold, in the second day, just one,... an so on.
Now I have the following query:
SELECT SUM(sal_quant)
FROM daily_sales
WHERE model_key='320D'
AND date_key IN (
SELECT date_key FROM car_release_dates WHERE model_key='320D')
But this only gives me the sum for the first release day. How can I get the next days?
Thanks.

Answer 1

I suppose there's no way a car could be sold before its release date. So you could simply group on the date_key:
SELECT date_key, SUM(sal_quant)
FROM daily_sales
WHERE model_key='320D'
GROUP BY date_key
ORDER BY date_key DESC
LIMIT 4
If it is possible to sell cars before the release date, add a WHERE clause:
AND date_key >= (
SELECT date_key FROM car_release_dates WHERE model_key='320D')
EDIT: Per your comment, you can constrain the query to within four days of multiple release dates with an INNER JOIN. For example:
SELECT ds.date_key, SUM(ds.sal_quant)
FROM daily_sales ds
INNER JOIN car_release_dates crd
ON crd.model_key = ds.model_key
AND ds.date_key BETWEEN crd.date_key
AND DATE_ADD(crd.date_key, INTERVAL 4 DAY)
WHERE ds.model_key='320D'
GROUP BY ds.date_key
ORDER BY ds.date_key DESC