You want to calculate a running average salary per department ordered by hire date. Which query correctly uses AVG() as a window function?

hard📝 Application Q8 of 15

PostgreSQL - Window Functions in PostgreSQL

ASELECT employee_id, department, salary, AVG(salary) OVER (PARTITION BY department ORDER BY hire_date ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS running_avg FROM employees;

BSELECT employee_id, department, salary, AVG(salary) OVER (ORDER BY hire_date PARTITION BY department) AS running_avg FROM employees;

CSELECT employee_id, department, salary, AVG(salary) OVER (PARTITION BY department) AS running_avg FROM employees;

DSELECT employee_id, department, salary, AVG(salary) FROM employees PARTITION BY department ORDER BY hire_date;

Step-by-Step Solution

Solution:

Step 1: Understand running average with window frame
To calculate running average, use AVG() OVER with PARTITION BY department, ORDER BY hire_date, and frame ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW.
Step 2: Validate syntax
SELECT employee_id, department, salary, AVG(salary) OVER (PARTITION BY department ORDER BY hire_date ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS running_avg FROM employees; correctly uses all required clauses in correct order and frame specification.
Final Answer:
SELECT employee_id, department, salary, AVG(salary) OVER (PARTITION BY department ORDER BY hire_date ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS running_avg FROM employees; -> Option A
Quick Check:
Running average needs frame clause with ORDER BY [OK]

Quick Trick: Use ROWS BETWEEN for running calculations [OK]

Common Mistakes:

Swapping PARTITION BY and ORDER BY order
Omitting window frame for running average
Using aggregate AVG() without OVER()

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You want to calculate a running average salary per department ordered by hire date. Which query correctly uses AVG() as a window function?

Step 1: Understand running average with window frame

Step 2: Validate syntax

Final Answer:

Quick Check:

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