SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic WHERE demographic.discharge_location = "DISCH-TRAN TO PSYCH HOSP" AND demographic.age < "77"
how many patients whose discharge location is disch-tran to psych hosp and age is less than 77?
CREATE TABLE diagnoses (
    subject_id text,
    hadm_id text,
    icd9_code text,
    short_title text,
    long_title text
)

CREATE TABLE demographic (
    subject_id text,
    hadm_id text,
    name text,
    marital_status text,
    age text,
    dob text,
    gender text,
    language text,
    religion text,
    admission_type text,
    days_stay text,
    insurance text,
    ethnicity text,
    expire_flag text,
    admission_location text,
    discharge_location text,
    diagnosis text,
    dod text,
    dob_year text,
    dod_year text,
    admittime text,
    dischtime text,
    admityear text
)

CREATE TABLE procedures (
    subject_id text,
    hadm_id text,
    icd9_code text,
    short_title text,
    long_title text
)

CREATE TABLE lab (
    subject_id text,
    hadm_id text,
    itemid text,
    charttime text,
    flag text,
    value_unit text,
    label text,
    fluid text
)

CREATE TABLE prescriptions (
    subject_id text,
    hadm_id text,
    icustay_id text,
    drug_type text,
    drug text,
    formulary_drug_cd text,
    route text,
    drug_dose text
)