“Insert if not exists” statement in SQLite

Question

If you never want to have duplicates, you should declare this as a table constraint:

CREATE TABLE bookmarks(
    users_id INTEGER,
    lessoninfo_id INTEGER,
    UNIQUE(users_id, lessoninfo_id)
);

(A primary key over both columns would have the same effect.)

It is then possible to tell the database that you want to silently ignore records that would violate such a constraint:

INSERT OR IGNORE INTO bookmarks(users_id, lessoninfo_id) VALUES(123, 456)