Question

I have a table with unique usernames and a bunch of string data I am keeping track of. Each user will have 1000 rows and when I select them I want to return them in the order they were added. Is the following code a necessary and correct way of doing this:

CREATE TABLE foo (
  username TEXT PRIMARY KEY,
  col1 TEXT,
  col2 TEXT,
  ...
  order_id INTEGER NOT NULL
);

CREATE INDEX foo_order_index ON foo(order_id);

SELECT * FROM foo where username = 'bar' ORDER BY order_id;

Answer 1

If each user will have 1000 rows, then username should not be the primary key. One option is to use the int identity column which all tables have (which optimizes I/O reads since it’s typically stored in that order).

Read under “RowIds and the Integer Primary Key” @ http://www.sqlite.org/lang_createtable.html

The data for each table in SQLite is stored as a B-Tree structure
containing an entry for each table row, using the rowid value as the
key. This means that retrieving or sorting records by rowid is fast.

Because it’s stored in that order in the B-tree structure, it should be fast to order by the int primary key. Make sure it’s an alias for rowid though – more in that article.

Also, if you’re going to be doing queries where username = ‘bob’, you should consider an index on the username column – especially there’s going to be many users which makes the index effective because of high selectivity. In contrast, adding an index on a column with values like 1 and 0 only leads to low selectivity and renders the index very ineffective. So, if you have 3 users 🙂 it’s not worth it.