CREATE TABLE chartevents (row_id DECIMAL, subject_id DECIMAL, hadm_id DECIMAL, icustay_id DECIMAL, itemid DECIMAL, charttime TIME, valuenum DECIMAL, valueuom TEXT)
CREATE TABLE procedures_icd (row_id DECIMAL, subject_id DECIMAL, hadm_id DECIMAL, icd9_code TEXT, charttime TIME)
CREATE TABLE d_items (row_id DECIMAL, itemid DECIMAL, label TEXT, linksto TEXT)
CREATE TABLE admissions (row_id DECIMAL, subject_id DECIMAL, hadm_id DECIMAL, admittime TIME, dischtime TIME, admission_type TEXT, admission_location TEXT, discharge_location TEXT, insurance TEXT, language TEXT, marital_status TEXT, ethnicity TEXT, age DECIMAL)
CREATE TABLE d_icd_procedures (row_id DECIMAL, icd9_code TEXT, short_title TEXT, long_title TEXT)
CREATE TABLE transfers (row_id DECIMAL, subject_id DECIMAL, hadm_id DECIMAL, icustay_id DECIMAL, eventtype TEXT, careunit TEXT, wardid DECIMAL, intime TIME, outtime TIME)
CREATE TABLE inputevents_cv (row_id DECIMAL, subject_id DECIMAL, hadm_id DECIMAL, icustay_id DECIMAL, charttime TIME, itemid DECIMAL, amount DECIMAL)
CREATE TABLE outputevents (row_id DECIMAL, subject_id DECIMAL, hadm_id DECIMAL, icustay_id DECIMAL, charttime TIME, itemid DECIMAL, value DECIMAL)
CREATE TABLE microbiologyevents (row_id DECIMAL, subject_id DECIMAL, hadm_id DECIMAL, charttime TIME, spec_type_desc TEXT, org_name TEXT)
CREATE TABLE icustays (row_id DECIMAL, subject_id DECIMAL, hadm_id DECIMAL, icustay_id DECIMAL, first_careunit TEXT, last_careunit TEXT, first_wardid DECIMAL, last_wardid DECIMAL, intime TIME, outtime TIME)
CREATE TABLE d_labitems (row_id DECIMAL, itemid DECIMAL, label TEXT)
CREATE TABLE diagnoses_icd (row_id DECIMAL, subject_id DECIMAL, hadm_id DECIMAL, icd9_code TEXT, charttime TIME)
CREATE TABLE patients (row_id DECIMAL, subject_id DECIMAL, gender TEXT, dob TIME, dod TIME)
CREATE TABLE cost (row_id DECIMAL, subject_id DECIMAL, hadm_id DECIMAL, event_type TEXT, event_id DECIMAL, chargetime TIME, cost DECIMAL)
CREATE TABLE d_icd_diagnoses (row_id DECIMAL, icd9_code TEXT, short_title TEXT, long_title TEXT)
CREATE TABLE prescriptions (row_id DECIMAL, subject_id DECIMAL, hadm_id DECIMAL, startdate TIME, enddate TIME, drug TEXT, dose_val_rx TEXT, dose_unit_rx TEXT, route TEXT)
CREATE TABLE labevents (row_id DECIMAL, subject_id DECIMAL, hadm_id DECIMAL, itemid DECIMAL, charttime TIME, valuenum DECIMAL, valueuom TEXT)

how much magnesium sulfate was prescribed for the first time on their last hospital visit to patient 44451?
SELECT prescriptions.dose_val_rx FROM prescriptions WHERE prescriptions.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 44451 AND NOT admissions.dischtime IS NULL ORDER BY admissions.admittime DESC LIMIT 1) AND prescriptions.drug = 'magnesium sulfate' ORDER BY prescriptions.startdate LIMIT 1
SELECT "prescriptions"."dose_val_rx" FROM "prescriptions" WHERE "prescriptions"."drug" = 'magnesium sulfate' AND "prescriptions"."hadm_id" IN (SELECT "admissions"."hadm_id" FROM "admissions" WHERE "admissions"."subject_id" = 44451 AND NOT "admissions"."dischtime" IS NULL ORDER BY "admissions"."admittime" DESC NULLS LAST LIMIT 1) ORDER BY "prescriptions"."startdate" NULLS FIRST LIMIT 1