SQL Exercises: Find the number of salesmen for each customer

SQL Aggregate Functions: Exercise-3 with Solution

From the following table, write a SQL query that counts the number of unique salespeople. Return number of salespeople.

Sample table: orders

Sample Solution:

SELECT COUNT (DISTINCT salesman_id) 
FROM orders;

Output of the Query:

count
6

Code Explanation:

The given SQL query that retrieve the number of unique values in the "salesman_id" column from the 'orders' table. The "SELECT COUNT (DISTINCT salesman_id)" statement specifies that the number of unique values in the "salesman_id" column should be counted.
By using the keyword "DISTINCT", it is ensured that only unique values will be counted and duplicate values will not be added to the final result in any way.
The result of this query will be a single value that represents the number of unique values in the "salesman_id" column in the 'orders' table.

Relational Algebra Expression:

Relational Algebra Tree:

Explanation:

visual presentation:

Practice Online

Query Visualization:

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