[Solved] What will be the output of this query?SELECT employee_id, salary, LEAD(salary, 2) OVER (ORDER BY employee_id) AS salary_after_two FROM employees; | PostgreSQL

PostgreSQL - Window Functions in PostgreSQL

What will be the output of this query?

SELECT employee_id, salary, LEAD(salary, 2) OVER (ORDER BY employee_id) AS salary_after_two FROM employees;

AShows salary and salary from previous two rows ordered by employee_id

BShows salary and salary from two rows ahead ordered by employee_id

CShows salary and salary from next row only

DCauses an error because offset 2 is invalid

Step-by-Step Solution

Solution:

Step 1: Understand LEAD with offset
LEAD(salary, 2) returns the salary value two rows ahead in the order defined by employee_id.
Step 2: Analyze output
Each row shows current salary and salary from two rows after it. If no such row exists, NULL is returned.
Final Answer:
Shows salary and salary from two rows ahead ordered by employee_id -> Option B
Quick Check:
LEAD with offset 2 returns value two rows forward [OK]

Quick Trick: LEAD(column, n) gets value n rows ahead [OK]

Common Mistakes:

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What will be the output of this query?