Give the station pressure status recorded by the weather station which contained no.12 store on 2012/5/15.
no.12 store refers to store_nbr = 12; on 2012/5/15 refers to date = '2012-05-15'; station pressure status refers to stnpressure
SELECT T1.stnpressure FROM weather AS T1 INNER JOIN relation AS T2 ON T1.station_nbr = T2.station_nbr WHERE T1.`date` = '2012-05-15' AND T2.store_nbr = 12
CREATE TABLE sales_in_weather
(
    date      DATE,
    store_nbr INTEGER,
    item_nbr  INTEGER,
    units     INTEGER,
    primary key (store_nbr, date, item_nbr)
);
CREATE TABLE weather
(
    station_nbr INTEGER,
    date        DATE,
    tmax        INTEGER,
    tmin        INTEGER,
    tavg        INTEGER,
    depart      INTEGER,
    dewpoint    INTEGER,
    wetbulb     INTEGER,
    heat        INTEGER,
    cool        INTEGER,
    sunrise     TEXT,
    sunset      TEXT,
    codesum     TEXT,
    snowfall    REAL,
    preciptotal REAL,
    stnpressure REAL,
    sealevel    REAL,
    resultspeed REAL,
    resultdir   INTEGER,
    avgspeed    REAL,
    primary key (station_nbr, date)
);
CREATE TABLE relation
(
    store_nbr   INTEGER
            primary key,
    station_nbr INTEGER,
    foreign key (store_nbr) references sales_in_weather(store_nbr),
    foreign key (station_nbr) references weather(station_nbr)
);
