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

ord_no      purch_amt   ord_date    customer_id  salesman_id
----------  ----------  ----------  -----------  -----------
70001       150.5       2012-10-05  3005         5002
70009       270.65      2012-09-10  3001         5005
70002       65.26       2012-10-05  3002         5001
70004       110.5       2012-08-17  3009         5003
70007       948.5       2012-09-10  3005         5002
70005       2400.6      2012-07-27  3007         5001
70008       5760        2012-09-10  3002         5001
70010       1983.43     2012-10-10  3004         5006
70003       2480.4      2012-10-10  3009         5003
70012       250.45      2012-06-27  3008         5002
70011       75.29       2012-08-17  3003         5007
70013       3045.6      2012-04-25  3002         5001

Sample Solution:

-- This query counts the number of distinct 'salesman_id' values.
SELECT COUNT(DISTINCT salesman_id)
-- Specifies the table from which to retrieve the data (in this case, 'orders').
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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