C#

private bool ColumnEqual(object A, object B)<br />
{<br />
	<br />
        // Compares two values to see if they are equal. Also compares DBNULL.Value.<br />
        // Note: If your DataTable contains object fields, then you must extend this<br />
        // function to handle them in a meaningful way if you intend to group on them.<br />
			<br />
        if ( A == DBNull.Value && B == DBNull.Value ) //  both are DBNull.Value<br />
            return true; <br />
        if ( A == DBNull.Value || B == DBNull.Value ) //  only one is DBNull.Value<br />
            return false; <br />
        return ( A.Equals(B) );  // value type standard comparison<br />
}

public DataTable SelectDistinct(string TableName, DataTable SourceTable, string FieldName)<br />
{	<br />
        DataTable dt = new DataTable(TableName);<br />
        dt.Columns.Add(FieldName, SourceTable.Columns[FieldName].DataType);<br />
			<br />
        object LastValue = null; <br />
        foreach (DataRow dr in SourceTable.Select("", FieldName))<br />
        {<br />
            if (  LastValue == null || !(ColumnEqual(LastValue, dr[FieldName])) ) <br />
            {<br />
                LastValue = dr[FieldName]; <br />
                dt.Rows.Add(new object[]{LastValue});<br />
            }<br />
        }<br />
        if (ds != null) <br />
            ds.Tables.Add(dt);<br />
        return dt;<br />
}