[INST] Here is a database schema:
customers :
CustomerID [ INTEGER ] primary_key
Segment [ TEXT ]
Currency [ TEXT ]

gasstations :
GasStationID [ INTEGER ] primary_key
ChainID [ INTEGER ]
Country [ TEXT ]
Segment [ TEXT ]

products :
ProductID [ INTEGER ] primary_key
Description [ TEXT ]

transactions_1k :
TransactionID [ INTEGER ] primary_key
Date [ DATE ]
Time [ TEXT ]
CustomerID [ INTEGER ]
CardID [ INTEGER ]
GasStationID [ INTEGER ]
ProductID [ INTEGER ]
Amount [ INTEGER ]
Price [ REAL ]

yearmonth :
CustomerID [ INTEGER ] yearmonth.CustomerID = customers.CustomerID
Date [ TEXT ]
Consumption [ REAL ]

Please write me a SQL statement that answers the following question: Which customers, paying in CZK, consumed the most gas in 2011? [/INST]
SELECT T1.CustomerID FROM customers AS T1 INNER JOIN yearmonth AS T2 ON T1.CustomerID = T2.CustomerID WHERE T1.Currency = 'CZK' GROUP BY T1.CustomerID ORDER BY SUM(T2.Consumption) DESC LIMIT 1;