### Database Schema:
CREATE TABLE gasstations (
	GasStationID	INTEGER	NOT NULL	PRIMARY KEY,
	ChainID	INTEGER	NULL,
	Country	TEXT	NULL,
	Segment	TEXT	NULL
);

CREATE TABLE customers (
	CustomerID	INTEGER	NOT NULL	PRIMARY KEY,
	Segment	TEXT	NULL,
	Currency	TEXT	NULL
);

CREATE TABLE yearmonth (
	CustomerID	INTEGER	NOT NULL	PRIMARY KEY,
	Date	TEXT	NOT NULL	PRIMARY KEY,
	Consumption	REAL	NULL,
	foreign key (CustomerID) references customers (CustomerID)
);

CREATE TABLE products (
	ProductID	INTEGER	NOT NULL	PRIMARY KEY,
	Description	TEXT	NULL
);

CREATE TABLE transactions_1k (
	TransactionID	INTEGER	NULL	PRIMARY KEY,
	Date	DATE	NULL,
	Time	TEXT	NULL,
	CustomerID	INTEGER	NULL,
	CardID	INTEGER	NULL,
	GasStationID	INTEGER	NULL,
	ProductID	INTEGER	NULL,
	Amount	INTEGER	NULL,
	Price	REAL	NULL
);

### User's Query:
Which customers, paying in CZK, consumed the most gas in 2011?

### Extra Knowledge:
Year 2011 can be presented as Between 201101 And 201112, which means between January and December in 2011
SELECT T1.CustomerID FROM customers AS T1 INNER JOIN yearmonth AS T2 ON T1.CustomerID = T2.CustomerID WHERE T1.Currency = 'CZK' AND T2.Date BETWEEN 201101 AND 201112 GROUP BY T1.CustomerID ORDER BY SUM(T2.Consumption) DESC LIMIT 1