VB.Net - Efficient way of de-duplicating data - vb.net

Question

I am dealing with a legacy application which is written in VB.Net 2.0 against a SQL 2000 database.
There is a single table which has ~125,000 rows and 2 pairs of fields with similar data.
i.e. FieldA1, FieldB1, FieldA2, FieldB2
I need to process a combined, distinct list of FieldA, FieldB.
Using SQL I have confirmed that there are ~140,000 distinct rows.
Due to a very restrictive framework in the application I can only retrieve the data as either 2 XML objects, 2 DataTable objects or 2 DataTableReader objects. I am unable to execute custom SQL using the framework.
Due to a very restrictive DB access policy I am unable to add a View or Stored Proc to retrieve as a single list.
What is the most efficient way to combine the 2 XML / DataTable / DataTableReader objects into a single, distinct, IEnumerable object for later processing?

Answer 1

I may have missed something here but could you not combine both DataTables using Merge?
DataTableA.Merge(DataTableB)
You can then use DataTableA.AsEnumerable()
Then see this answer on how to remove duplicates or
You can do this with a DataView as follows: dt.DefaultView.ToTable(True,[Column names])

Answer 2

This is the solution I came up with.
Combine the 2 DataTables using .Merge (thanks to Matt's answer)
Using this as a base I came up with the following code to get distinct rows from the DataTable based on 2 columns:
Private Shared Function GetDistinctRows(sourceTable As DataTable, ParamArray columnNames As String()) As DataTable
Dim dt As New DataTable
Dim sort = String.Empty
For Each columnName As String In columnNames
dt.Columns.Add(columnName, sourceTable.Columns(columnName).DataType)
If sort.Length > 0 Then
sort = sort & ","
End If
sort = sort & columnName
Next
Dim lastValue As DataRow = Nothing
For Each dr As DataRow In sourceTable.Select("", sort)
Dim add As Boolean = False
If IsNothing(lastValue) Then
add = True
Else
For Each columnName As String In columnNames
If Not (lastValue(columnName).Equals(dr(columnName))) Then
add = True
Exit For
End If
Next
End If
If add Then
lastValue = dr
dt.ImportRow(dr)
End If
Next
Return dt
End Function