表中名称相同但ID不同的值的总和

I am using mySql and C# to create a Expense Manager. It records Expenses with Expenses_ID and YearMonth . Now how can I SUM the Expenses with same Expenses_ID of different YearMonthID -eg. Total 'Electricity Bill' (Expense_ID=1) Costs of year 2012 (2012 jan, 2012 feb, 2012 mar)I am using mySql and C# to create a Expense Man