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Chapter 3 of 7
Every write pays
The order lookup is fast now. The team wants indexes on customer and date too, then the Monday rush brings new orders.
This chapter: What does each index cost when a new order is written?
About this chapter
You will learn
- An insert updates every index
- Full leaves split in two
- Why unused indexes are pure cost
Words you’ll meet
- Insert
- Writing a new row into a table.
- Page split
- When a full page gets a new key, it splits in two and its parent gains an entry.
Step 1 of 4
A new order is an : one row written to the table’s last page. With no index, that is all.
Write a new order.
The SQL
INSERT INTO orders (id, customer, day, status)
VALUES (10001, 398, DATE '2026-01-01' + 296, 'open');