PostgreSQL Aggregate Functions and Group By: Get the average salary for all departments working more than 10 employees

14. Write a query to get the average salary for all departments working more than 10 employees.

Sample Solution:

Code:

SELECT department_id, AVG(salary), COUNT(*) 
FROM employees 
GROUP BY department_id 
HAVING COUNT(*) > 10;

Sample table: employees

Output:

pg_exercises=# SELECT department_id, AVG(salary), COUNT(*)
pg_exercises-# FROM employees
pg_exercises-# GROUP BY department_id
pg_exercises-# HAVING COUNT(*) > 10;
 department_id |          avg          | count
---------------+-----------------------+-------
            80 | 8955.8823529411764706 |    34
            50 | 3475.5555555555555556 |    45
(2 rows)

Relational Algebra Expression:

Relational Algebra Tree:

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