Question

I have 3 tables

Table: Products
                productid (int)
                name (varchar)
                description (text)

Table: Sales
                salesid (int)
                productid (int)

Table: Links
                linkid (int)
                productid (int)

Now, I need a query that can get me total number of product-ids that are either present in sales table, or links table or both.

Help appreciated.

Thanks

Answer 1

As long as the data is proper, you dont really need to check the products table

SELECT COUNT(1) 
FROM (SELECT distinct ProductId
      from Sales
     UNION -- instead of union all to ensure that only distinct values are taken
      SELECT distinct ProductId
      from Links) products