Database schema:

CREATE TABLE "transaction" (
	"TransactionID" INTEGER -- example: ['100000', '100001'],
	"CreditCardNumber" INTEGER -- example: ['6011583832864739', '4716634257568793'],
	"CustomerID" INTEGER -- example: ['864896', '610766'],
	"TransactionDate" DATE -- example: ['2014-07-07', '2014-07-13'],
	"CreditCardType" TEXT -- example: ['Discover', 'Visa'],
	"LocationID" INTEGER -- example: ['2', '1'],
	"RootBeerID" INTEGER -- example: ['105798', '105661'],
	"PurchasePrice" REAL -- example: ['1.0', '3.0'],
	PRIMARY KEY ("TransactionID"), 
	CONSTRAINT fk_transaction_customers FOREIGN KEY("CustomerID") REFERENCES customers ("CustomerID"),
	CONSTRAINT fk_transaction_location FOREIGN KEY("LocationID") REFERENCES location ("LocationID"),
	CONSTRAINT fk_transaction_rootbeer FOREIGN KEY("RootBeerID") REFERENCES rootbeer ("RootBeerID")
)


CREATE TABLE customers (
	"CustomerID" INTEGER -- example: ['103508', '101811'],
	"First" TEXT -- example: ['Kenneth', 'Madeleine'],
	"Last" TEXT -- example: ['Walton', 'Jones'],
	"StreetAddress" TEXT -- example: ['6715 Commonwealth Dr', '3603 Leola Way'],
	"City" TEXT -- example: ['Sacramento', 'Orangevale'],
	"State" TEXT -- example: ['CA'],
	"ZipCode" INTEGER -- example: ['94256', '94258'],
	"Email" TEXT -- example: ['j_madeleine@gmail.com', 'walton.k76@fastmail.com'],
	"PhoneNumber" TEXT -- example: ['(916) 918-1561', '(916) 186-9423'],
	"FirstPurchaseDate" DATE -- example: ['2013-05-30', '2013-02-06'],
	"SubscribedToEmailList" TEXT -- example: ['FALSE', 'TRUE'],
	"Gender" TEXT -- example: ['M', 'F'],
	PRIMARY KEY ("CustomerID")
)


CREATE TABLE geolocation (
	"LocationID" INTEGER -- example: ['0', '1'],
	"Latitude" REAL -- example: ['0.0', '38.566129'],
	"Longitude" REAL -- example: ['0.0', '-121.426432'],
	PRIMARY KEY ("LocationID"), 
	CONSTRAINT fk_geolocation_location FOREIGN KEY("LocationID") REFERENCES location ("LocationID")
)


CREATE TABLE location (
	"LocationID" INTEGER -- example: ['0', '1'],
	"LocationName" TEXT -- example: ['Sac State American River Courtyard', 'LOST'],
	"StreetAddress" TEXT -- example: ['6000 J St'],
	"City" TEXT -- example: ['Sacramento'],
	"State" TEXT -- example: ['CA'],
	"ZipCode" INTEGER -- example: ['95819'],
	PRIMARY KEY ("LocationID"), 
	CONSTRAINT fk_location_geolocation FOREIGN KEY("LocationID") REFERENCES geolocation ("LocationID")
)


CREATE TABLE rootbeer (
	"RootBeerID" INTEGER -- example: ['100000', '100001'],
	"BrandID" INTEGER -- example: ['10002', '10001'],
	"ContainerType" TEXT -- example: ['Can', 'Bottle'],
	"LocationID" INTEGER -- example: ['2', '1'],
	"PurchaseDate" DATE -- example: ['2015-07-03', '2016-05-09'],
	PRIMARY KEY ("RootBeerID"), 
	CONSTRAINT fk_rootbeer_geolocation FOREIGN KEY("LocationID") REFERENCES geolocation ("LocationID"),
	CONSTRAINT fk_rootbeer_location FOREIGN KEY("LocationID") REFERENCES location ("LocationID"),
	CONSTRAINT fk_rootbeer_rootbeerbrand FOREIGN KEY("BrandID") REFERENCES rootbeerbrand ("BrandID")
)


CREATE TABLE rootbeerbrand (
	"BrandID" INTEGER -- example: ['10002', '10001'],
	"BrandName" TEXT -- example: ['A&W', 'A.J. Stephans'],
	"FirstBrewedYear" INTEGER -- example: ['1919', '1926'],
	"BreweryName" TEXT -- example: ['AJ Stephans Beverages', 'Dr Pepper Snapple Group'],
	"City" TEXT -- example: ['Fall River', 'Lodi'],
	"State" TEXT -- example: ['MA', 'CA'],
	"Country" TEXT -- example: ['Australia', 'United States'],
	"Description" TEXT -- example: ['After setting up the first A&W Root Beer stand in ', 'AJ Stephans Company makes \nthe finest elixirs and '],
	"CaneSugar" TEXT -- example: ['FALSE', 'TRUE'],
	"CornSyrup" TEXT -- example: ['FALSE', 'TRUE'],
	"Honey" TEXT -- example: ['FALSE', 'TRUE'],
	"ArtificialSweetener" TEXT -- example: ['FALSE', 'TRUE'],
	"Caffeinated" TEXT -- example: ['FALSE', 'TRUE'],
	"Alcoholic" TEXT -- example: ['FALSE'],
	"AvailableInCans" TEXT -- example: ['FALSE', 'TRUE'],
	"AvailableInBottles" TEXT -- example: ['FALSE', 'TRUE'],
	"AvailableInKegs" TEXT -- example: ['FALSE', 'TRUE'],
	"Website" TEXT -- example: ['http://www.rootbeer.com/', 'http://www.ajstephans.com/'],
	"FacebookPage" TEXT -- example: ['https://www.facebook.com/Dads-Old-Fashioned-Root-B', 'https://www.facebook.com/Dog-N-Suds-Bottled-Root-B'],
	"Twitter" TEXT -- example: ['https://twitter.com/ilovedads', 'https://twitter.com/1919rootbeer'],
	"WholesaleCost" REAL -- example: ['0.42', '0.98'],
	"CurrentRetailPrice" REAL -- example: ['1.0', '3.0'],
	PRIMARY KEY ("BrandID")
)


CREATE TABLE rootbeerreview (
	"CustomerID" INTEGER -- example: ['105549', '101811'],
	"BrandID" INTEGER -- example: ['10012', '10014'],
	"StarRating" INTEGER -- example: ['5', '1'],
	"ReviewDate" DATE -- example: ['2013-07-15', '2013-07-08'],
	"Review" TEXT -- example: ['You could have done better Sactown.', 'Too much bite, not enough barq.'],
	PRIMARY KEY ("CustomerID", "BrandID"), 
	CONSTRAINT fk_rootbeerreview_customers FOREIGN KEY("CustomerID") REFERENCES customers ("CustomerID"),
	CONSTRAINT fk_rootbeerreview_rootbeerbrand FOREIGN KEY("BrandID") REFERENCES rootbeerbrand ("BrandID")
)

Question: Which brand of root beer has the lowest unit profit available to wholesalers? Indicate the ID of the customer that has the highest number of purchases of the said brand.
Evidence: brand of root beer refers to BrandName; lowest unit profit available to wholesalers refers to MIN(SUBTRACT(CurrentRetailPrice, WholesaleCost)); ID of the customer refers to CustomerID; highest number of purchases refers to MAX(COUNT(CustomerID));

SQL:
SELECT T3.BrandName, T2.CustomerID FROM rootbeer AS T1 INNER JOIN `transaction` AS T2 ON T1.RootBeerID = T2.RootBeerID INNER JOIN rootbeerbrand AS T3 ON T1.BrandID = T3.BrandID GROUP BY T3.BrandID ORDER BY T3.CurrentRetailPrice - T3.WholesaleCost, COUNT(T1.BrandID) DESC LIMIT 1