[Solved] Given the table Sales with columns id and amount, what will this query return?SELECT id, amount, LAG(amount) OVER (ORDER BY id) AS prev_amount FROM Sales; | SQL

SQL - Advanced Window Functions

Given the table Sales with columns id and amount, what will this query return?

SELECT id, amount, LAG(amount) OVER (ORDER BY id) AS prev_amount FROM Sales;

AEach row shows its amount and the amount from the previous row ordered by id

BEach row shows its amount and the amount from the next row ordered by id

CEach row shows the sum of current and previous amounts

DEach row shows only the current amount without previous data

Step-by-Step Solution

Solution:

Step 1: Understand LAG with ORDER BY
The query uses LAG(amount) to get the previous row's amount based on id order.
Step 2: Interpret the output
Each row will have its own amount and the amount from the row before it in id order; the first row's previous amount will be NULL.
Final Answer:
Each row shows its amount and the amount from the previous row ordered by id -> Option A
Quick Check:
LAG returns previous row value in order [OK]

Quick Trick: LAG returns previous row's value in ORDER BY sequence [OK]

Common Mistakes:

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