What is a database index? Find one row without reading them all

Ask a database for one person among a million rows and it could read every row until it finds them. That is slow. An index is the database's shortcut: a sorted list of one column that points back to each row, like the index at the back of a book.

Step through a search with and without an index, then see a real SQLite query plan switch from a scan to an index search.