Solution:Step 1: Analyze the WINDOW clauseThe window named w partitions rows by department and orders by employee.Step 2: Understand AVG() OVER w behaviorAVG(salary) OVER w calculates the average salary for rows in the same department up to the current employee in order.Final Answer:The average sala

[Solved] Given the query:SELECT department, employee, salary, AVG(salary) OVER w AS avg_salary FROM employees WINDOW w AS (PARTITION BY department ORDER BY employee) ORDER BY department, employee;What does... | PostgreSQL

PostgreSQL - Window Functions in PostgreSQL

Given the query:

SELECT department, employee, salary, AVG(salary) OVER w AS avg_salary
FROM employees
WINDOW w AS (PARTITION BY department ORDER BY employee)
ORDER BY department, employee;

What does the avg_salary column show?

AThe average salary of employees in the same department up to the current employee

BThe average salary of all employees in the company

CThe average salary of employees partitioned by department without order

DThe average salary of employees ordered by employee name across all departments

Step-by-Step Solution

Solution:

Step 1: Analyze the WINDOW clause
The window named w partitions rows by department and orders by employee.
Step 2: Understand AVG() OVER w behavior
AVG(salary) OVER w calculates the average salary for rows in the same department up to the current employee in order.
Final Answer:
The average salary of employees in the same department up to the current employee -> Option A
Quick Check:
Partition + order = running average per department [OK]

Quick Trick: Partition + order means running calculation per group [OK]

Common Mistakes:

Ignoring ORDER BY in window
Assuming average over entire table
Confusing partition with no partition

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Given the query:

Step 1: Analyze the WINDOW clause

Step 2: Understand AVG() OVER w behavior

Final Answer:

Quick Check:

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