SQL Exercises: Number of non NULL city values for salesmen

Last update on December 20 2024 11:33:41 (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

Query Visualization:

Duration:

Rows:

Cost:

Note: The pictorial represetation above is based on hypothetical table for the purpose of explanation only. Your answer may not match.

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