Question

I have a pseudo SQL statement like

select [orderid], [productname], [price], [productid_FK]
from Order

This will give me 5 rows:

So the result is 5 rows of which 3 have a [productid_FK] of “2”. This FK-column references to the table called [Product].

Now lets say I want an extra column based on the [productid_FK].

The column must contain the total number of products in another table called [products]

Can I achieve this by enchaning the current pseudo query?

Answer 1

One way to get the results is a subquery. There are several ways to do this depending on the DB. I often do it this way

SELECT o.[orderid], 
       o.[productname], 
       o.[price], 
       [productid_FK], 
       p_counts.k 
FROM   order o 
       INNER JOIN (SELECT productid_fk, 
                          COUNT(product_id) k 
                   FROM   products 
                   GROUP  BY productid_fk) p_counts 
         ON o.productid_fk = p_counts.productid_fk