How many patients with a normal anti-SSA came to the hospital before 1990?
normal anti-SSA refers to SSA IN('-','+-'); came to the hospital before 1990 refers to YEAR(`First Date`) < 1990; Should compute the number of distinct ones
SELECT COUNT(DISTINCT T1.ID) FROM Patient AS T1 INNER JOIN Laboratory AS T2 ON T1.ID = T2.ID WHERE T2.SSA IN ('negative', '0') AND STRFTIME('%Y', T2.Date) < '1990'