[Solved] Consider the table employees with columns department, role, and salary. What does this query return?SELECT department, role, AVG(salary) FROM employees GROUP BY department, role; | PostgreSQL

PostgreSQL - Aggregate Functions and GROUP BY

Consider the table employees with columns department, role, and salary. What does this query return?

SELECT department, role, AVG(salary) FROM employees GROUP BY department, role;

AAverage salary for all employees without grouping

BAverage salary for each department only

CAverage salary for each role only

DAverage salary for each department and role combination

Step-by-Step Solution

Solution:

Step 1: Identify grouping columns
The query groups by both department and role, so groups are unique pairs of these columns.
Step 2: Understand aggregation
AVG(salary) calculates average salary per group, here per department-role pair.
Final Answer:
Average salary for each department and role combination -> Option D
Quick Check:
GROUP BY multiple columns with AVG = average per combination [OK]

Quick Trick: AVG with GROUP BY multiple columns averages per combo [OK]

Common Mistakes:

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Consider the table employees with columns department, role, and salary. What does this query return?