When the planner skips your index

The team adds an index on date for the warehouse’s reports. Today’s orders come back fast; this month’s report is no faster.

This chapter: Why would the database ignore an index you built?

About this chapter

You will learn

The planner guesses each way’s cost first
An index fetches its rows one by one
Past a small share of rows, a scan wins

Words you’ll meet

Planner: The part of the database that picks how to run each request, before running it.
Estimated rows: The planner’s guess of how many rows a request matches, from statistics it keeps.

Step 1 of 5

Before each request the guesses every way’s page reads from its , then picks the cheapest.

Ask for today’s orders.

The SQL

CREATE INDEX ON orders (day);

SELECT * FROM orders WHERE day = DATE '2026-01-01' + 296;

SELECT * FROM orders
WHERE day BETWEEN DATE '2026-01-01' + 273 AND DATE '2026-01-01' + 296;