SQL Exercises: Customers whose grade differs from a London customer

SQL SUBQUERY: Exercise-28 with Solution

28. From the following tables write a SQL query to find those customers whose grades are not the same as those who live in London City. Return customer_id, cust_name, city, grade and salesman_id.

customer_id  cust_name     city        grade       salesman_id
-----------  ------------  ----------  ----------  -----------
3002         Nick Rimando  New York    100         5001
3005         Graham Zusi   California  200         5002
3001         Brad Guzan    London      100         5005
3004         Fabian Johns  Paris       300         5006
3007         Brad Davis    New York    200         5001
3009         Geoff Camero  Berlin      100         5003
3008         Julian Green  London      300         5002
3003         Jozy Altidor  Moncow      200         5007

Sample Solution:

-- Selecting all columns from the 'customer' table
SELECT *
-- Specifying the table to retrieve data from ('customer')
FROM customer
-- Filtering the results based on the condition that 'grade' is not equal to all values in the set of 'grade' returned by a subquery
WHERE grade <> ALL 
   -- Subquery: Selecting 'grade' values from the 'customer' table where 'city' is 'London' and 'grade' is not null
   (SELECT grade FROM customer WHERE city='London' AND NOT grade IS NULL);

Output of the Query:

customer_id	cust_name		city		grade	salesman_id
3002		Nick Rimando		New York	100	5001
3007		Brad Davis		New York	200	5001
3005		Graham Zusi		California	200	5002
3009		Geoff Cameron		Berlin		100	5003
3003		Jozy Altidor		Moscow		200	5007

Explanation:

The said SQL query is selecting all columns and rows from the 'customer' table where the grade is not equal to all of the grades found in the subquery.
The subquery is selecting the grade from the 'customer' table where the city is equal to 'London' and the grade is not null. So the main query is getting the rows of all customers whose grade is not equal to all grades of customers living in London.

Visual Explanation:

Practice Online

Sample Database: inventory

Query Visualization:

Duration:

Rows:

Cost:

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