instruction: provide the number of patients whose diagnoses icd9 code is v452 and lab test fluid is pleural?
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN diagnoses ON demographic.hadm_id = diagnoses.hadm_id INNER JOIN lab ON demographic.hadm_id = lab.hadm_id WHERE diagnoses.icd9_code = "V452" AND lab.fluid = "Pleural"