SQL Exercises: Number of non NULL city values for salesmen

Last update on February 11 2025 08:02:08 (UTC/GMT +8 hours)

From the following table, write a SQL query to count the number of salespeople in a city. Return number of salespeople.

Sample table: salesman

 salesman_id |    name    |   city   | commission 
-------------+------------+----------+------------
        5001 | James Hoog | New York |       0.15
        5002 | Nail Knite | Paris    |       0.13
        5005 | Pit Alex   | London   |       0.11
        5006 | Mc Lyon    | Paris    |       0.14
        5007 | Paul Adam  | Rome     |       0.13
        5003 | Lauson Hen | San Jose |       0.12

Sample Solution :

-- This query counts the number of rows in the 'salesman' table where the 'city' is not NULL.
SELECT COUNT(*)
-- Specifies the table from which to retrieve the data (in this case, 'salesman').
FROM salesman
-- Filters the rows to only include those where the 'city' is not NULL.
WHERE city IS NOT NULL;

Output of the Query:

count
6

Code Explanation:

The said SQL query to count the number of rows in the 'salesman' table where the "city" column is not NULL. The "COUNT(*)" function counts the number of rows in the table, and the "WHERE city IS NOT NULL" clause specifies that only rows where the "city" column is not NULL should be counted.

Relational Algebra Expression:

Relational Algebra Tree:

Explanation :

Visual presentation:

Practice Online

For more Practice: Solve these Related Problems:

• Write a SQL query to count the number of salespeople in the city 'London'.
• Write a SQL query to count the number of salespeople in the city 'Paris', but only for salespeople with a commission rate of 0.13 or higher.
• Write a SQL query to count the number of salespeople in the city 'New York', but only for salespeople who have made at least one sale.
• Write a SQL query to count the number of salespeople in the city 'San Jose', but only for salespeople with a commission rate of 0.12 or lower.

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