How many of the patients born in 1920s had pneumonia?
patients born in 1920s refer to patient where birthdate like '192%'; pneumonia refers to DESCRIPTION = 'Pneumonia' from conditions;
SELECT COUNT(DISTINCT T1.patient) FROM patients AS T1 INNER JOIN conditions AS T2 ON T1.patient = T2.PATIENT WHERE DESCRIPTION = 'Pneumonia' AND strftime('%Y', T1.birthdate) LIKE '192%'