PostgreSQL Aggregate Functions and Group By: Get the average salary and number of employees working in a particular designation

5. Write a query to get the average salary and number of employees working in the department which ID is 90.

Sample Solution:

Code:

SELECT AVG(salary),count(*) 
FROM employees 
WHERE department_id = 90;

Sample table: employees

Output:

pg_exercises=# SELECT AVG(salary),count(*)
pg_exercises-# FROM employees
pg_exercises-# WHERE department_id = 90;
        avg         | count
--------------------+-------
 19363.333333333333 |     3
(1 row)

Relational Algebra Expression:

Relational Algebra Tree:

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