How to append one DataTable to another DataTable

I would like to append one DataTable to another DataTable. I see the DataTable class has two methods; "Load(IDataReader)" and "Merge(DataTable)". From the documentation, both appear to 'merge' the incoming data with the existing DataTable if rows exist. I will be doing the merge in a data access layer.

I could use an IDataReader and use the Load method to merge the DataTables. Or I could load a DataSet using the IDataReader, get the DataTable from the DataSet, and then use the Merge method to merge the DataTables.

I was wondering if someone could tell me which is the proper method to use?

Alternatively, let me know if you have a different suggestion on how to accomplish this task.

The datatype in the same columns name must be equals.

dataTable1.Merge(dataTable2);

After that the result is:

dataTable1 = dataTable1 + dataTable2

Merge takes a DataTable, Load requires an IDataReader - so depending on what your data layer gives you access to, use the required method. My understanding is that Load will internally call Merge, but not 100% sure about that.

If you have two DataTables, use Merge.

You could let your DataAdapter do the work. DataAdapter.Fill(DataTable) will append your new rows to any existing rows in DataTable.

Add two datasets containing datatables, now it will merge as required

DataSet ds1 = new DataSet();
DataSet ds2 = new DataSet();

DataTable dt1 = new DataTable();
dt1.Columns.Add(new DataColumn("Column1", typeof(System.String)));

DataRow newSelRow1 = dt1.NewRow();
newSelRow1["Column1"] = "Select";
dt1.Rows.Add(newSelRow1);

DataTable dt2 = new DataTable();
dt2.Columns.Add(new DataColumn("Column1", typeof(System.String)));

DataRow newSelRow2 = dt1.NewRow();
newSelRow2["Column1"] = "DataRow1Data";  // Data
dt2.Rows.Add(newSelRow2);

ds1.Tables.Add(dt1);
ds2.Tables.Add(dt2);

ds1.Tables[0].Merge(ds2.Tables[0]);

Now ds1 will have the merged data

Consider a solution that will neatly handle arbitrarily many tables.

//ASSUMPTION: All tables must have the same columns
var tables = new List<DataTable>();
tables.Add(oneTableToRuleThemAll);
tables.Add(oneTableToFindThem);
tables.Add(oneTableToBringThemAll);
tables.Add(andInTheDarknessBindThem);
//Or in the real world, you might be getting a collection of tables from some abstracted data source.

//behold, a table too great and terrible to imagine
var theOneTable = tables.SelectMany(dt => dt.AsEnumerable()).CopyToDataTable();

Encapsulated into a helper for future reuse:

public static DataTable CombineDataTables(params DataTable[] args)
{
	return args.SelectMany(dt => dt.AsEnumerable()).CopyToDataTable();
}

Just have a few tables declared in code?

var combined = CombineDataTables(dt1,dt2,dt3);

Want to combine into one of the existing tables instead of creating a new one?

dt1 = CombineDataTables(dt1,dt2,dt3);

Already have a collection of tables, instead of declared one by one?

//Pretend variable tables already exists
var tables = new[] { dt1, dt2, dt3 };
var combined = CombineDataTables(tables);

use loop

  for (int i = 0; i < dt1.Rows.Count; i++)
        {      
           dt2.Rows.Add(dt1.Rows[i][0], dt1.Rows[i][1], ...);//you have to insert all Columns...
        }