This JOIN method is equivalent to the TSQL INNER JOIN expression using equality.

This method returns all columns from both tables.
Once again, column name collision is avoided by appending "_Second" to the columns affected.

There are a total of 3 signatures for this method.
In summary the code works as follows:

Create new empty table
Create a DataSet and add tables.
Get a reference to Join columns
Create a DataRelation
Construct JOIN table columns
Using the DataRelation add rows with matching related rows using array manipulation
Return table

//FJC = First Join Column

//SJC = Second Join Column

public static DataTable Join (DataTable First, DataTable Second, DataColumn[] FJC, DataColumn[] SJC)

{

//Create Empty Table

DataTable table = new DataTable("Join");

// Use a DataSet to leverage DataRelation

using(DataSet ds = new DataSet())

{

//Add Copy of Tables

ds.Tables.AddRange(new DataTable[]{First.Copy(),Second.Copy()});

//Identify Joining Columns from First

DataColumn[] parentcolumns = new DataColumn[FJC.Length];

for(int i = 0; i < parentcolumns.Length; i++)

{

parentcolumns[i] = ds.Tables[0].Columns[FJC[i].ColumnName];

}

//Identify Joining Columns from Second

DataColumn[] childcolumns = new DataColumn[SJC.Length];

for(int i = 0; i < childcolumns.Length; i++)

{

childcolumns[i] = ds.Tables[1].Columns[SJC[i].ColumnName];

}

//Create DataRelation

DataRelation r = new DataRelation(string.Empty,parentcolumns,childcolumns,false);

ds.Relations.Add(r);

//Create Columns for JOIN table

for(int i = 0; i < First.Columns.Count; i++)

{

table.Columns.Add(First.Columns[i].ColumnName, First.Columns[i].DataType);

}

for(int i = 0; i < Second.Columns.Count; i++)

{

//Beware Duplicates

if(!table.Columns.Contains(Second.Columns[i].ColumnName))

table.Columns.Add(Second.Columns[i].ColumnName, Second.Columns[i].DataType);

else

table.Columns.Add(Second.Columns[i].ColumnName + "_Second", Second.Columns[i].DataType);

}

//Loop through First table

table.BeginLoadData();

foreach(DataRow firstrow in ds.Tables[0].Rows)

{

//Get "joined" rows

DataRow[] childrows = firstrow.GetChildRows(r);

if(childrows != null && childrows.Length > 0)

{

object[] parentarray = firstrow.ItemArray;

foreach(DataRow secondrow in childrows)

{

object[] secondarray = secondrow.ItemArray;

object[] joinarray = new object[parentarray.Length+secondarray.Length];

Array.Copy(parentarray,0,joinarray,0,parentarray.Length);

Array.Copy(secondarray,0,joinarray,parentarray.Length,secondarray.Length);

table.LoadDataRow(joinarray,true);

}

}

}

table.EndLoadData();

}

return table;

}

public static DataTable Join (DataTable First, DataTable Second, DataColumn FJC, DataColumn SJC)

{

return SQLOps.Join(First, Second, new DataColumn[]{FJC}, new DataColumn[]{SJC});

}

public static DataTable Join (DataTable First, DataTable Second, string FJC, string SJC)

{

return SQLOps.Join(First, Second, new DataColumn[]{First.Columns[FJC]}, new DataColumn[]{First.Columns[SJC]});

}