Database schema:

CREATE TABLE central_superstore (
	"Row ID" INTEGER -- example: ['2', '1'],
	"Order ID" TEXT -- example: ['CA-2011-112326', 'CA-2011-103800'],
	"Order Date" DATE -- example: ['2013-01-04', '2013-01-03'],
	"Ship Date" DATE -- example: ['2013-01-07', '2013-01-08'],
	"Ship Mode" TEXT -- example: ['First Class', 'Standard Class'],
	"Customer ID" TEXT -- example: ['PO-19195', 'DP-13000'],
	"Region" TEXT -- example: ['Central'],
	"Product ID" TEXT -- example: ['OFF-PA-10000174', 'OFF-LA-10003223'],
	"Sales" REAL -- example: ['11.784', '16.448'],
	"Quantity" INTEGER -- example: ['2', '3'],
	"Discount" REAL -- example: ['0.2', '0.8'],
	"Profit" REAL -- example: ['5.5512', '4.2717'],
	PRIMARY KEY ("Row ID"), 
	CONSTRAINT fk_central_superstore_people FOREIGN KEY("Customer ID", "Region") REFERENCES people ("Customer ID", "Region"),
	CONSTRAINT fk_central_superstore_product FOREIGN KEY("Product ID", "Region") REFERENCES product ("Product ID", "Region")
)


CREATE TABLE east_superstore (
	"Row ID" INTEGER -- example: ['4648', '4647'],
	"Order ID" TEXT -- example: ['CA-2011-130092', 'CA-2011-141817'],
	"Order Date" DATE -- example: ['2013-01-11', '2013-01-05'],
	"Ship Date" DATE -- example: ['2013-01-14', '2013-01-12'],
	"Ship Mode" TEXT -- example: ['First Class', 'Standard Class'],
	"Customer ID" TEXT -- example: ['MB-18085', 'SV-20365'],
	"Region" TEXT -- example: ['East'],
	"Product ID" TEXT -- example: ['OFF-AR-10003478', 'FUR-FU-10000010'],
	"Sales" REAL -- example: ['9.94', '19.536'],
	"Quantity" INTEGER -- example: ['2', '3'],
	"Discount" REAL -- example: ['0.2', '0.0'],
	"Profit" REAL -- example: ['3.0814', '4.884'],
	PRIMARY KEY ("Row ID"), 
	CONSTRAINT fk_east_superstore_people FOREIGN KEY("Customer ID", "Region") REFERENCES people ("Customer ID", "Region"),
	CONSTRAINT fk_east_superstore_product FOREIGN KEY("Product ID", "Region") REFERENCES product ("Product ID", "Region")
)


CREATE TABLE people (
	"Customer ID" TEXT -- example: ['AA-10315', 'AA-10375'],
	"Customer Name" TEXT -- example: ['Alex Avila', 'Allen Armold'],
	"Segment" TEXT -- example: ['Consumer', 'Home Office'],
	"Country" TEXT -- example: ['United States'],
	"City" TEXT -- example: ['Round Rock', 'Omaha'],
	"State" TEXT -- example: ['Texas', 'Nebraska'],
	"Postal Code" INTEGER -- example: ['68104', '78664'],
	"Region" TEXT -- example: ['East', 'Central'],
	PRIMARY KEY ("Customer ID", "Region")
)


CREATE TABLE product (
	"Product ID" TEXT -- example: ['FUR-BO-10000112', 'FUR-BO-10000330'],
	"Product Name" TEXT -- example: ['Sauder Inglewood Library Bookcases', 'Sauder Camden County Barrister Bookcase, Planked C'],
	"Category" TEXT -- example: ['Office Supplies', 'Furniture'],
	"Sub-Category" TEXT -- example: ['Chairs', 'Bookcases'],
	"Region" TEXT -- example: ['South', 'Central'],
	PRIMARY KEY ("Product ID", "Region")
)


CREATE TABLE south_superstore (
	"Row ID" INTEGER -- example: ['10344', '10343'],
	"Order ID" TEXT -- example: ['CA-2011-167199', 'CA-2011-106054'],
	"Order Date" DATE -- example: ['2013-01-06', '2013-01-10'],
	"Ship Date" DATE -- example: ['2013-01-07', '2013-01-10'],
	"Ship Mode" TEXT -- example: ['First Class', 'Standard Class'],
	"Customer ID" TEXT -- example: ['JO-15145', 'ME-17320'],
	"Region" TEXT -- example: ['South'],
	"Product ID" TEXT -- example: ['FUR-CH-10004063', 'OFF-AR-10002399'],
	"Sales" REAL -- example: ['12.78', '2573.82'],
	"Quantity" INTEGER -- example: ['9', '3'],
	"Discount" REAL -- example: ['0.0', '0.7'],
	"Profit" REAL -- example: ['746.4078', '5.2398'],
	PRIMARY KEY ("Row ID"), 
	CONSTRAINT fk_south_superstore_people FOREIGN KEY("Customer ID", "Region") REFERENCES people ("Customer ID", "Region"),
	CONSTRAINT fk_south_superstore_product FOREIGN KEY("Product ID", "Region") REFERENCES product ("Product ID", "Region")
)


CREATE TABLE west_superstore (
	"Row ID" INTEGER -- example: ['13583', '13584'],
	"Order ID" TEXT -- example: ['CA-2011-157147', 'CA-2011-130813'],
	"Order Date" DATE -- example: ['2013-01-06', '2013-01-13'],
	"Ship Date" DATE -- example: ['2013-01-18', '2013-01-08'],
	"Ship Mode" TEXT -- example: ['Standard Class', 'Second Class'],
	"Customer ID" TEXT -- example: ['BD-11605', 'LS-17230'],
	"Region" TEXT -- example: ['West'],
	"Product ID" TEXT -- example: ['OFF-PA-10002005', 'OFF-ST-10000078'],
	"Sales" REAL -- example: ['19.44', '1325.85'],
	"Quantity" INTEGER -- example: ['5', '3'],
	"Discount" REAL -- example: ['0.0', '0.15'],
	"Profit" REAL -- example: ['238.653', '9.3312'],
	PRIMARY KEY ("Row ID"), 
	CONSTRAINT fk_west_superstore_people FOREIGN KEY("Customer ID", "Region") REFERENCES people ("Customer ID", "Region"),
	CONSTRAINT fk_west_superstore_product 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?
Evidence: 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