### Database Schema
CREATE TABLE people
(
    "Customer ID"   TEXT,
    "Customer Name" TEXT,
    Segment         TEXT,
    Country         TEXT,
    City            TEXT,
    State           TEXT,
    "Postal Code"   INTEGER,
    Region          TEXT,
    primary key ("Customer ID", Region)
)

CREATE TABLE product
(
    "Product ID"   TEXT,
    "Product Name" TEXT,
    Category       TEXT,
    "Sub-Category" TEXT,
    Region         TEXT,
    primary key ("Product ID", Region)
)

CREATE TABLE central_superstore
(
    "Row ID"      INTEGER
            primary key,
    "Order ID"    TEXT,
    "Order Date"  DATE,
    "Ship Date"   DATE,
    "Ship Mode"   TEXT,
    "Customer ID" TEXT,
    Region        TEXT,
    "Product ID"  TEXT,
    Sales         REAL,
    Quantity      INTEGER,
    Discount      REAL,
    Profit        REAL,
    foreign key ("Customer ID", Region) references people("Customer ID",Region),
    foreign key ("Product ID", Region) references product("Product ID",Region)
)

CREATE TABLE east_superstore
(
    "Row ID"      INTEGER
            primary key,
    "Order ID"    TEXT,
    "Order Date"  DATE,
    "Ship Date"   DATE,
    "Ship Mode"   TEXT,
    "Customer ID" TEXT,
    Region        TEXT,
    "Product ID"  TEXT,
    Sales         REAL,
    Quantity      INTEGER,
    Discount      REAL,
    Profit        REAL,
    foreign key ("Customer ID", Region) references people("Customer ID",Region),
    foreign key ("Product ID", Region) references product("Product ID",Region)
)

CREATE TABLE south_superstore
(
    "Row ID"      INTEGER
            primary key,
    "Order ID"    TEXT,
    "Order Date"  DATE,
    "Ship Date"   DATE,
    "Ship Mode"   TEXT,
    "Customer ID" TEXT,
    Region        TEXT,
    "Product ID"  TEXT,
    Sales         REAL,
    Quantity      INTEGER,
    Discount      REAL,
    Profit        REAL,
    foreign key ("Customer ID", Region) references people("Customer ID",Region),
    foreign key ("Product ID", Region) references product("Product ID",Region)
)

CREATE TABLE west_superstore
(
    "Row ID"      INTEGER
            primary key,
    "Order ID"    TEXT,
    "Order Date"  DATE,
    "Ship Date"   DATE,
    "Ship Mode"   TEXT,
    "Customer ID" TEXT,
    Region        TEXT,
    "Product ID"  TEXT,
    Sales         REAL,
    Quantity      INTEGER,
    Discount      REAL,
    Profit        REAL,
    foreign key ("Customer ID", Region) references people("Customer ID",Region),
    foreign key ("Product ID", Region) references product("Product ID",Region)
)

### Question
Among the customers from Chicago, Illinois, what is the highest quantity of products bought in a single order?

### Hint
from Chicago refers to City = 'Chicago'; Illinois refers to State = 'Illinois'; highest quantity refers to max(Quantity)

### SQL
SELECT T1.Quantity FROM west_superstore AS T1 INNER JOIN east_superstore AS T2 ON T1.`Customer ID` = T2.`Customer ID` INNER JOIN central_superstore AS T3 ON T3.`Customer ID` = T2.`Customer ID` INNER JOIN south_superstore AS T4 ON T4.`Customer ID` = T3.`Customer ID` INNER JOIN people AS T5 ON T5.`Customer ID` = T4.`Customer ID` WHERE T5.City = 'Chicago' AND T5.State = 'Illinois' ORDER BY T1.Quantity DESC LIMIT 1