How to manage multiple price lists and items in different MySql tables with Php?

Question

I have to manage multiple price lists with different validity start date.

How can I select only the prices with the correct validity date from the price list table?
If an item has more than one price I must only take the most recent one but with a date no later than today! I hope I explained myself..

Normally I use the INNER JOIN but in this case I do not know how to select the data properly.

I need someting like this:

SELECT * FROM $item_table  
LEFT JOIN $price_table ON $item_table.product_code = $price_table.product_code  
WHERE ($price_table.validity_date /*is the most recent but no later than today*/ )

I give you an example of table structure:

Items table
+-------+--------------+-------------+  
| Brand | Product Code | Description |  
+-------+--------------+-------------+  
| XXX   | XXX-123      | Lorem ipsum |  
| XXX   | XXX-456      | Lorem ipsum |  
| YYY   | YYY-123      | Lorem ipsum |  
| YYY   | YYY-456      | Lorem ipsum |  
| ZZZ   | ZZZ-123      | Lorem ipsum |  
+-------+--------------+-------------+

Price lists table
+-------+--------------+-------+---------------------+
| Brand | Product Code | Price | Validity Start Date |
+-------+--------------+-------+---------------------+
| XXX   | XXX-123      | 10.00 | 2016/01/01          |
| YYY   | YYY-123      | 20.00 | 2016/01/01          |
| XXX   | XXX-123      | 12.00 | 2017/01/01          | <- I need this one
| YYY   | YYY-123      | 22.00 | 2017/01/01          | <- I need this one
| XXX   | XXX-123      | 15.00 | 2018/01/01          |
| YYY   | YYY-123      | 25.00 | 2018/01/01          |
+-------+--------------+-------+---------------------+

Unfortunately, I can not put a price validity end date because when I put it in, I do not know when the next price list will be loaded. Otherwise, it would have been easier.

I accept any suggestion on a different way to structure the price lists table if this can lead to simpler solutions!

Answer 1

You need to find the one and only product that matches the following rules :

• Brand is $brand
• Product code is $code
• Start date is before CURDATE()
• Start date is the highest ( MAX() ) of the previous matches

So if I only wanted the price here's how I would formulate my query :

SELECT `Price`
FROM `Price lists`
WHERE `Brand` = :brand
AND `Product Code` = :productCode
AND `Validity Start Date` = (
    SELECT MAX(`Validity Start Date`)
    FROM `Price lists`
    WHERE `Brand` = :brand
    AND `Product Code` = :productCode
    AND `Validity Start Date` < CURDATE()
)

EDIT : Added the filter on Brand and Product Code in the inner function

RE-EDIT : So if you need a full table of all products with the correct price in each line it gives the following query

SELECT a.*, b.Price, b.`Validity Start Date`
FROM Items a
LEFT JOIN (
    SELECT `Product Code`, `Validity Start Date`, Price
    FROM `Price lists`
    WHERE `Validity Start Date` < CURDATE()
) b ON a.`Product Code` = b.`Product Code`
WHERE b.`Validity Start Date` = (
    SELECT MAX(`Validity Start Date`)
    FROM `Price lists`
    WHERE `Product Code` = a.`Product Code`
    AND `Validity Start Date` < CURDATE()
)

Answer 2

SELECT MIN(test.diff),test.* FROM (SELECT *,DATEDIFF(`Validity Start Date`,CURDATE())as diff FROM `Price_lists_table` LEFT JOIN $price_table ON $item_table.product_code = $price_table.product_code  WHERE DATEDIFF(`Validity Start Date`,CURDATE()) >0 ) as test;