PostgreSQL Basic SELECT Statement: Get unique department ID from employee table

2. Write a query to get a unique department ID from employee table.

Sample Solution:

Code:

-- This SQL query selects unique values from the 'department_id' column in the 'employees' table.

SELECT DISTINCT department_id 
FROM employees;

Explanation:

• The SELECT DISTINCT statement is used to retrieve unique values from a specified column or columns in a table.
• department_id is the name of the column being selected from the employees table.
• This query retrieves unique values of department IDs from the 'employees' table. It eliminates duplicate values and returns only distinct values of the 'department_id' column.

Sample table: employees

Output:

pg_exercises=# SELECT DISTINCT department_id 
pg_exercises-# FROM employees;

 department_id
---------------
            90
            20
           100
            40
           110
            80
            70
            50
            60
            30
            10
             0
(12 rows)

Relational Algebra Expression:

Relational Algebra Tree:

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Previous: Write a query to display the names (first_name, last_name) using an alias name "First Name", "Last Name".
Next: Write a query to get the details of all employees from the employee table in descending order by their first name.