Select value based on a test
Use a CASE if you want, but you can always check if COUNT() > 0

SELECT usl.*, 
    CASE WHEN COUNT(blip.id) &gt; 0 THEN TRUE ELSE FALSE END as blacklisted
FROM user_session_logs as usl
LEFT JOIN blacklisted_ips as blip ON blip.ip_address = usl.ip_address
GROUP BY usl.id;