instruction: how many patients on dialys route of drug administration have a diagnoses of knee joint replacement?
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN diagnoses ON demographic.hadm_id = diagnoses.hadm_id INNER JOIN prescriptions ON demographic.hadm_id = prescriptions.hadm_id WHERE diagnoses.long_title = "Knee joint replacement" AND prescriptions.route = "DIALYS"