[ Team LiB ] Recipe Using Expression Columns to Display Aggregate Values Problem You want to add summary information such as averages, sums, and counts to a table based on related child rows. Solution Use expression columns to perform aggregate calculations based on child rows. | Team LiB Recipe Using Expression Columns to Display Aggregate Values Problem You want to add summary information such as averages sums and counts to a table based on related child rows. Solution Use expression columns to perform aggregate calculations based on child rows. The sample code starts by creating a DataSet containing the Orders and Order Details tables from Northwind sample database and a relation between them. An expression is added to the Order Details table to calculate the extended price for each row. Aggregate values for the total extended price of the order and the number of Order Detail rows are added to the Orders table. Finally the default view of the Orders table is bound to the data grid to display the results. The C code is shown in Example 3-7. Example 3-7. File Namespaces variables and constants using System using using using Table name constants private const String ORDERS_TABLE Orders private const String ORDERDETAILS_TABLE OrderDetails Relation name constants private const String ORDERS_ORDERDETAILS_RELATION Orders_OrderDetails_Relation Field name constants private const String ORDERID_FIELD OrderlD H . . . DataSet ds new DataSet SqlDataAdapter da Fill the Order table and add it to the DataSet. da new SqlDataAdapter SELECT FROM Orders Sql_ConnectString DataTable orderTable new DataTable ORDERS_TABLE orderTable . Add orderT able Fill the OrderDetails table and add it to the DataSet. da new SqlDataAdapter SELECT FROM Order Details Sql_ConnectString DataTable orderDetailTable new DataTable ORDERDETAILS_TABLE orderDetailTable orderDetailTable Create a relation between the tables. ORDERS_ORDERDETAILS_RELATION ORDERS_TABLE .Columns ORDERID_FIELD ORDERDETAILS_TABLE .Columns ORDERID_FIELD true Create the expression column .
