Which customers, paying in CZK, consumed the most gas in 2011?
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