Schema:
CREATE TABLE inputevents_cv (
    row_id number,
    subject_id number,
    hadm_id number,
    icustay_id number,
    charttime time,
    itemid number,
    amount number
)

CREATE TABLE chartevents (
    row_id number,
    subject_id number,
    hadm_id number,
    icustay_id number,
    itemid number,
    charttime time,
    valuenum number,
    valueuom text
)

CREATE TABLE outputevents (
    row_id number,
    subject_id number,
    hadm_id number,
    icustay_id number,
    charttime time,
    itemid number,
    value number
)

CREATE TABLE d_items (
    row_id number,
    itemid number,
    label text,
    linksto text
)

CREATE TABLE prescriptions (
    row_id number,
    subject_id number,
    hadm_id number,
    startdate time,
    enddate time,
    drug text,
    dose_val_rx text,
    dose_unit_rx text,
    route text
)

CREATE TABLE icustays (
    row_id number,
    subject_id number,
    hadm_id number,
    icustay_id number,
    first_careunit text,
    last_careunit text,
    first_wardid number,
    last_wardid number,
    intime time,
    outtime time
)

CREATE TABLE procedures_icd (
    row_id number,
    subject_id number,
    hadm_id number,
    icd9_code text,
    charttime time
)

CREATE TABLE d_labitems (
    row_id number,
    itemid number,
    label text
)

CREATE TABLE transfers (
    row_id number,
    subject_id number,
    hadm_id number,
    icustay_id number,
    eventtype text,
    careunit text,
    wardid number,
    intime time,
    outtime time
)

CREATE TABLE patients (
    row_id number,
    subject_id number,
    gender text,
    dob time,
    dod time
)

CREATE TABLE admissions (
    row_id number,
    subject_id number,
    hadm_id number,
    admittime time,
    dischtime time,
    admission_type text,
    admission_location text,
    discharge_location text,
    insurance text,
    language text,
    marital_status text,
    ethnicity text,
    age number
)

CREATE TABLE d_icd_diagnoses (
    row_id number,
    icd9_code text,
    short_title text,
    long_title text
)

CREATE TABLE diagnoses_icd (
    row_id number,
    subject_id number,
    hadm_id number,
    icd9_code text,
    charttime time
)

CREATE TABLE d_icd_procedures (
    row_id number,
    icd9_code text,
    short_title text,
    long_title text
)

CREATE TABLE labevents (
    row_id number,
    subject_id number,
    hadm_id number,
    itemid number,
    charttime time,
    valuenum number,
    valueuom text
)

CREATE TABLE cost (
    row_id number,
    subject_id number,
    hadm_id number,
    event_type text,
    event_id number,
    chargetime time,
    cost number
)

CREATE TABLE microbiologyevents (
    row_id number,
    subject_id number,
    hadm_id number,
    charttime time,
    spec_type_desc text,
    org_name text
)

Question: what is the dose of sodium bicarbonate that is first prescribed to patient 10811 since 05/2103?

SQL:
SELECT prescriptions.dose_val_rx FROM prescriptions WHERE prescriptions.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 10811) AND prescriptions.drug = 'sodium bicarbonate' AND STRFTIME('%y-%m', prescriptions.startdate) >= '2103-05' ORDER BY prescriptions.startdate LIMIT 1