[Solved] You see this EXPLAIN output:Nested Loop (cost=0.00..37.50 rows=5 width=200)But the query runs very slowly. What could be a reason? | PostgreSQL

PostgreSQL - Performance Tuning

You see this EXPLAIN output:

Nested Loop  (cost=0.00..37.50 rows=5 width=200)

But the query runs very slowly. What could be a reason?

AThe query uses a sequential scan on a small table

BThe query is missing a GROUP BY clause

CThe EXPLAIN output is incorrect

DThe Nested Loop is joining large tables without indexes

Step-by-Step Solution

Solution:

Step 1: Understand Nested Loop behavior
Nested Loops can be slow if joining large tables without indexes.
Step 2: Evaluate other options
GROUP BY absence or small table scans don't explain slowness here.
Final Answer:
The Nested Loop is joining large tables without indexes -> Option D
Quick Check:
Slow Nested Loop = Large join without indexes [OK]

Quick Trick: Nested Loops slow on large joins without indexes [OK]

Common Mistakes:

Master "Performance Tuning" in PostgreSQL

9 interactive learning modes - each teaches the same concept differently

You see this EXPLAIN output: