SQL-根据日期范围获取最低价格

Question

I have a database containing prices from various suppliers for the same product. Each supplier/product combination has a start & end date with a product ID and price

id | pid | aid | start_date | end_date | price
1  | 1   |  1  | 2017-01-01 | 2017-01-10 | 10.00
1  | 1   |  2  | 2017-01-01 | 2017-01-05 | 12.00
1  | 1   |  2  | 2017-01-06 | 2017-01-09 | 9.00

I use a calendar table to make sure I have all the dates in a certain range. The struggle I have is to select the min price given a certain date range. The above data should output as below.

date       | aid | price
2017-01-01 | 1   | 10.00
2017-01-02 | 1   | 10.00
2017-01-03 | 1   | 10.00
2017-01-04 | 1   | 10.00
2017-01-05 | 1   | 10.00
2017-01-06 | 2   |  9.00
2017-01-07 | 2   |  9.00
2017-01-08 | 2   |  9.00
2017-01-09 | 2   |  9.00
2017-01-10 | 1   | 10.00

Just having one supplier and getting the price is not an issue, but as soon as I start grouping the data I only get one result or an incorrect result. I'm using this query, which provides the wrong outcome.

SELECT 
    c.date, min(p.price) as min_price 
FROM 
    bricks_calender c 
LEFT JOIN 
    bricks_prijzen p ON c.date BETWEEN p.start_date AND p.end_date
WHERE 
    p.pid = 1 
GROUP BY 
    aid 
ORDER BY 
    c.date

Any suggestion where I need to update this query, to get the expected outcome? Or should I change my data model (which is of course not preferred)

Answer 1

If bricks_calender contains one row per date, the follow should work:

SELECT 
    c.`date`, 
    (select s.`aid` from `bricks_prijzen` s where s.`price` = min(p.`price`) and c.`date` BETWEEN s.`start_date` AND s.`end_date` ORDER BY s.`price` ASC LIMIT 0,1) AS `aid`,
    min(p.`price`) as `min_price`
FROM `bricks_calender` c
LEFT JOIN `bricks_prijzen` p
    ON c.`date` BETWEEN p.`start_date` AND p.`end_date`
WHERE 
    p.`pid` = 1 
GROUP BY 
    c.`date`
ORDER BY 
    c.`date`;

Answer 2

I think it's simply because you group your data by aid with GROUP BY aid , so you can't have more row than the number of different aid that exist.

By unsetting this GROUP BY , does it solve the problem?