-- Followers: a user following another user. Public.
CREATE TABLE follows (
    id          TEXT PRIMARY KEY,
    follower_id TEXT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    followee_id TEXT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    created_at  BIGINT NOT NULL
);
CREATE UNIQUE INDEX idx_follows_pair ON follows (follower_id, followee_id);
CREATE INDEX idx_follows_followee ON follows (followee_id);