Select only rows where min(column1) and min (column2)

Question

I have two tables. The first table shows the id_product and product_price_value. Below I will show you one example (in my database there are many rows)

TABLE: main_product

ID_product: product_price_value: 
       119, Product1

TABLE: value_product

product_price_value: width_from: width_to: height_from: height_to: price: 
Product1           ,         10,       20,           5,        15,   100
Product1           ,         10,       20,          10,        30,   200
Product1           ,         20,       30,           5,        45,   300
Product1           ,         30,       30,          20,        30,   400

As you can see one product can have multiple dimensions. I want to get the price with the lowest width and height combined. In my example it should be the first row (width from -> 10, height from -> 5).

I used the following code:

$sql = "SELECT value_product.price FROM value_product INNER JOIN main_product
        ON (main_product.product_price_value = value_product.product_price_value
        AND (
         value_product.width_from = (SELECT MIN(value_product.width_from) FROM value_product) 
         AND value_product.height_from = (SELECT MIN(value_product.height_from) FROM value_product)
        )
);";

In this way I thought I was gonna get the price for the lowest width/height for each product. But the only results I get is when the width_from OR height_from contains a value of 0. If either width or height has more than 0 then it doesn't return anything.

Am I doing something wrong in my query?

Is there any way to get the price with the lowest 'width_from' and 'height_from' columns?

Thanks

Answer 1

If you only want such a price for one product, you can simply sort and limit:

SELECT   price
FROM     value_product
WHERE    product_price_value = ?
ORDER BY width_from + height_from
LIMIT    1

Otherwise you're after the group-wise minimum , which can be obtained by joining the table back to a grouped version of itself:

SELECT   v.product_price_value,
         v.price
FROM     value_product v
    JOIN (
           SELECT   product_price_value,
                    MIN(width_from + height_from) min_dimension
           FROM     value_product
           GROUP BY product_price_value
         ) t
      ON t.product_price_value = v.product_price_value
     AND t.min_dimension = v.width_from + v.height_from

In both cases I have assumed that there is only ever one record with the minimal dimensions. Should there be multiple such records, the first query will pick one indeterminately; and the second query will list them all. If this is not your desired behaviour, you will have to clarify what you would like to occur instead.