SQL EXISTS operator with GROUP BY

Question

I am currently looking through the EXISTS operator examples on http://www.w3resource.com/sql/special-operators/sql_exists.php# and have come across an example which doesn't quite make sense. The code is as follows:

SELECT cust_code,cust_name,cust_city,grade  
FROM customer  
WHERE grade=2 AND  
    EXISTS(  
        SELECT COUNT(*)
        FROM customer  
        WHERE grade=2  
        GROUP BY grade  
        HAVING COUNT(*)>2
    );

From my understanding, the subquery will always evaluate to TRUE and it doesn't relate to the customer table higher up - so it seems irrelevant to put it in there.

Can anybody explain what the code is trying to achieve here please?

Many Thanks!

Answer 1

EXISTS will evaluate to false when count of records with grade=2 is less than or equal to 2. Query checks if there are more than two records with grade=2. If there are then show columns mentioned in the outer select.