In a database system with an "orders" table, write a query to count the number of unique salespeople.Return the number of unique salespeople.

Sure, here is a SQL query that will return the number of unique salespeople from the "orders" table:

SELECT COUNT(DISTINCT salesperson) AS unique_salespeople
FROM orders;

Here's a step-by-step breakdown of the query:

1. SELECT: This keyword is used to select data from a database.

2. COUNT(DISTINCT salesperson): The COUNT function is used to count the number of rows that match a specified condition. The DISTINCT keyword is used in conjunction with COUNT to count only unique values, in this case, unique salespeople.

3. AS unique_salespeople: The AS keyword is used to rename a column or table with an alias. Here, it's used to rename the count of unique salespeople as "unique_salespeople".

4. FROM orders: The FROM keyword is used to specify the table from which to select the data, in this case, the "orders" table.