CREATE TABLE IF NOT EXISTS followed_users (
    follower_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    followed_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    PRIMARY KEY (follower_id, followed_id),
    CHECK (follower_id <> followed_id)
);

CREATE INDEX IF NOT EXISTS idx_followed_users_followed
    ON followed_users(followed_id, follower_id);