I have created a demo for multiple tables which returning duplicate data as well and after that merge into single table. See the code below:
SqlDataAdapter adapter = new SqlDataAdapter("procGetEmployee", sqlConn);
DataSet resultDS = new DataSet();
adapter.Fill(resultDS, "dsEmployees");
DataTable dtFinal = new DataTable("dtEmployee");
for (int i = 0; i < resultDS.Tables.Count; i++)
{
dtFinal.Merge(resultDS.Tables[i]);
}
Result: All tables merged into single table that is
dtFinal