For the patients whose anti-SSB are normal, how many of them have other symptoms observed in their examination?
anti-SSB are normal refers to SSB IN('-', '+-'); have other symptoms refers to Symptoms IS NOT NULL; Should compute the number of distinct ones
SELECT COUNT(DISTINCT T1.ID) FROM Examination AS T1 INNER JOIN Laboratory AS T2 ON T1.ID = T2.ID WHERE T2.SSB = 'negative' OR '0' AND T1.Symptoms IS NOT NULL