MySQL LEFT JOIN, GROUP BY and ORDER BY not working as required

Question

I have a table

\'products\' => (\'product_id\', \'name\', \'description\') 

and a table

\'product_price\' => (\'pro         


        

Answer 1

Mysqlism:

SELECT p.*, MAX(pp.date_updated), pp.price 
FROM products p 
LEFT JOIN product_price pp ON pp.product_id = p.product_id
GROUP BY p.product_id 

Will work on some RDBMS:

SELECT p.*, pp.date_updated, pp.price 
FROM products p 
LEFT JOIN product_price pp ON pp.product_id = p.product_id
WHERE (p.product_id, pp.date_updated) 

   in (select product_id, max(date_updated) 
       from product_price 
       group by product_id)

Will work on most RDBMS:

SELECT p.*, pp.date_updated, pp.price 
FROM products p 
LEFT JOIN product_price pp ON pp.product_id = p.product_id

WHERE EXISTS
(
    select null -- inspired by Linq-to-SQL style :-)
    from product_price 

    WHERE product_id = p.product_id 

    group by product_id

    HAVING max(date_updated) = pp.date_updated
)

Will work on all RDBMS:

SELECT p.*, pp.date_updated, pp.price 
FROM products p 
LEFT JOIN product_price pp ON pp.product_id = p.product_id

LEFT JOIN 
(
    select product_id, max(date_updated) as recent 
    from product_price 
    group by product_id
) AS latest 
ON latest.product_id = p.product_id AND latest.recent = pp.date_updated

And if nate c's code intent is to just get one row from product_price, no need to table-derive (i.e. join (select product_price_id, max(date_updated) from products_price) as pp_max), he might as well just simplify(i.e. no need to use the product_price_id surrogate primary key) it like the following:

SELECT p.*, pp.date_updated, pp.price 
FROM products p 
LEFT JOIN product_price pp ON pp.product_id = p.product_id
WHERE pp.date_updated = (select max(date_updated) from product_price)