Calculated column in DataSet

Avg is only an example. Aggregates are required in Compute methods. But, if You have relation 1:1 aggregates are doing nothing. You can convert string to other types using CONVERT function built-in Expression. See help for Expression property (DataColumn).

1. As far as I understand, Avg(...) returns averegae value of all rowcell values. I need real meanings. 2. What if this column will have DataType String?

Set relation between tables. Next, set Expression property of column as in help: If a table has more than one child, the syntax is: Child(RelationName). For example, if a table has two child tables named Customers and Orders, and the DataRelation object is named Customers2Orders, the reference would be: Avg(Child(Customers2Orders).Quantity) Add new column to DataGrid column styles, if You use them.

I understand it. But in this case I should run query with another one field. I wanted to leave query as it was but in top level datagrid's view insert column that represent data from another datatable. What you suggest is to have another copy of the column from datatable in another datatable.

I tried this and it worked . You could then fille the new column from another source. Len DataTable myTable= ds.Tables[0]; myTable.Columns.Add("Test");