[Solved] Consider this SQL snippet:SELECT * FROM foreign_table LIMIT 5;Assuming foreign_table is a foreign table via postgres_fdw connected to a remote PostgreSQL server, what happens when this query runs? | PostgreSQL

PostgreSQL - Advanced Features

Consider this SQL snippet:

SELECT * FROM foreign_table LIMIT 5;

Assuming foreign_table is a foreign table via postgres_fdw connected to a remote PostgreSQL server, what happens when this query runs?

APostgreSQL fetches only 5 rows from the remote table and returns them

BPostgreSQL fetches all rows from remote table then limits to 5 locally

CQuery fails because LIMIT is not supported on foreign tables

DPostgreSQL creates a local copy of the table with 5 rows

Step-by-Step Solution

Solution:

Step 1: Understand postgres_fdw query pushdown
postgres_fdw pushes down LIMIT to remote server to optimize data transfer.
Step 2: Analyze query behavior
Only 5 rows are fetched from remote server, not all rows then limited locally.
Final Answer:
PostgreSQL fetches only 5 rows from the remote table and returns them -> Option A
Quick Check:
FDW pushes LIMIT to remote = PostgreSQL fetches only 5 rows from the remote table and returns them [OK]

Quick Trick: FDW pushes LIMIT to remote server to reduce data [OK]

Common Mistakes:

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Consider this SQL snippet: