Why Covering indexes with INCLUDE in PostgreSQL? - Purpose & Use Cases

The Big Idea

What if your database could answer questions without flipping through extra pages every time?

The Scenario

Imagine you have a huge book and you want to find specific information quickly. Without an index, you have to flip through every page manually.

Now, suppose you create a simple list of page numbers for some topics, but when you look up a topic, you still need to open the book to get the details.

The Problem

Manually searching through all pages or even using a basic list wastes time and effort.

Every time you want details, you must open the book again, which slows you down and can cause mistakes if you lose your place.

The Solution

Covering indexes with INCLUDE add extra information directly to the index, so you don't have to open the book at all.

This means the database can answer your questions faster by looking only at the index, saving time and reducing errors.

Before vs After

✗ Before

CREATE INDEX idx_name ON table(column);
-- Query still reads table for extra columns

✓ After

CREATE INDEX idx_name ON table(column) INCLUDE (extra_column);
-- Query uses index only, no table read needed

What It Enables

It enables lightning-fast queries by storing all needed data in the index itself, avoiding extra lookups.

Real Life Example

In an online store, you want to quickly find products by category and show their prices without extra delays.

Using covering indexes with INCLUDE lets the system fetch category and price directly from the index, speeding up your shopping experience.

Key Takeaways

Manual searching or simple indexes require extra data lookups.

Covering indexes with INCLUDE store extra columns in the index.

This reduces query time and improves performance.