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

CREATE INDEX IF NOT EXISTS idx_user_blocks_blocked
ON user_blocks (blocked_id, blocker_id);