Question

I have two tables: a product table and a territory table. The product tables holds IDs of products and the territory code denoting which countries they can be sold in:

PRODUCT:

PRODUCT_ID  | TERRITORY_CODE
----------------------------
   PROD1    |       2
   PROD2    |       0
   PROD3    |       1
   PROD4    |       0
   PROD5    |       2
   PROD6    |       0
   PROD7    |       2

The second table table holds a territory code and the corresponding ISO code of countries it’s allowed to be sold in. For example:

TERRITORY:

TERRITORY_CODE | COUNTRY_CODE
---------------------------
      0        |     US
      1        |     CA
      2        |     US
      2        |     CA

I would like to write a query that counts the number of PRODUCT_IDs using COUNTRY_CODE as a key.

For example, I want to know how many distinct products there are for sale in the US. I don’t want to have to know that 0 and 2 are territory codes that contain the US, I just want to look up by COUNTRY_CODE. How can I do this?

In some preliminary research, I’ve found that a WITH clause may be useful, and came up with the following query:

WITH country AS (
  SELECT (DISTINCT COUNTRY_CODE)
  FROM TERRITORY
) 
SELECT COUNT(DISTINCT PRODUCT_ID) 
FROM country c,
PRODUCT p
WHERE p.TERRITORY_CODE=c.TERRITORY_ID;

However, this doesn’t produce the expected result. I also can’t get it to group by COUNTRY_CODE. What am I doing wrong?

Answer 1

Looks like you need to use GROUP BY. Try something like this:

SELECT T.Country_Code, COUNT(DISTINCT PRODUCT_ID) 
FROM Product P
JOIN Territory T ON P.Territory_Code = T.Territory_Code
GROUP BY T.Country_Code

And the SQL Fiddle.

Good luck.