Simon Willison’s Weblog

Modern SQLite: Generated columns (via) The second in Anton Zhiyanov's series on SQLite features you might have missed.

It turns out I had an incorrect mental model of generated columns. In SQLite these can be "virtual" or "stored" (written to disk along with the rest of the table, a bit like a materialized view). Anton noted that "stored are rarely used in practice", which surprised me because I thought that storing them was necessary for them to participate in indexes.

It turns out that's not the case. Anton's example here shows a generated column providing indexed access to a value stored inside a JSON key:

create table events (
  id integer primary key,
  event blob,
  etime text as (event ->> 'time'),
  etype text as (event ->> 'type')
);
create index events_time on events(etime);
insert into events(event) values (
  '{"time": "2024-05-01", "type": "credit"}'
);

Update: snej reminded me that this isn't a new capability either: SQLite has been able to create indexes on expressions for years.