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Chapter 1 of 7
Find one order
Larkspur’s order system keeps every order in one table. Customers wait on the orders page, and the team wants to know why.
This chapter: What does the database do to find a single order?
About this chapter
You will learn
- How a table is stored as pages of rows
- A full scan reads every page
- Why its cost grows with the table
Words you’ll meet
- Row
- One record in a table: here, one order.
- Page
- A fixed-size block of rows the database reads in one go: here, 50 orders.
- Full scan
- Reading every page of a table to find the rows a request wants.
Step 1 of 4
A customer asks about order 1042. With no index, the database checks every : a .
Find order 1042.
The SQL
SELECT * FROM orders WHERE id = 1042;