[Solved] What does the LAG function do in PostgreSQL? — Ans: Returns the value from a previous row in the same result set | PostgreSQL

PostgreSQL - Window Functions in PostgreSQL

What does the LAG function do in PostgreSQL?

AReturns the value from a previous row in the same result set

BReturns the value from the next row in the same result set

CDeletes the previous row in the table

DUpdates the current row with the previous row's value

Step-by-Step Solution

Solution:

Step 1: Understand the purpose of LAG
The LAG function is used to access data from a previous row in the same query result without using a self-join.
Step 2: Compare with other options
LEAD returns the next row's value, while LAG returns the previous row's value. Options C and D describe actions that LAG does not perform.
Final Answer:
Returns the value from a previous row in the same result set -> Option A
Quick Check:
LAG function = previous row value [OK]

Quick Trick: LAG looks backward, LEAD looks forward in rows [OK]

Common Mistakes:

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What does the LAG function do in PostgreSQL?