Index out of range exception unhandled vb.net - vb.net

Question

I just faced a problem with my code.It raises an exception.This is the code.
conn = oSubPayItemDescription.GetDbConnection()
md = New OleDbCommand("SELECT [sub_pay_item_quantity].[quantity],[sub_pay_item_unit_rate].[rate] FROM " &
"[sub_pay_item_quantity],[sub_pay_item_unit_rate] WHERE [sub_pay_item_quantity].[sub item]=[sub_pay_item_unit_rate].[sub item] AND " &
"[sub_pay_item_quantity].[sub item]='" & subItem & "' AND [sub_pay_item_quantity].[bridge type]='" & bridgeType & "' " &
"AND [sub_pay_item_quantity].[span]='" & span & "'", conn)
data_reader = cmd.ExecuteReader()
If data_reader.HasRows = True Then
Do While data_reader.Read()
payItem = CDbl(data_reader.Item("pay item"))
subpayItem = CDbl(data_reader.Item("sub pay item"))
subItem = data_reader.Item("sub item")
unit = data_reader.Item("unit")
bridgeType = data_reader.Item("bridge type")
span = (data_reader.Item("span").ToString())
quantity = CDbl(data_reader.Item("quantity"))
rate = CDbl(data_reader.Item("rate"))
RichTextBox1.AppendText(payItem & vbTab & vbTab & " " & " " & subpayItem & vbTab & vbTab & subItem & vbTab & vbTab & " " & _
unit & vbTab & vbTab & " " & " " & " " & " " & bridgeType & vbTab & vbTab & " " & span & vbTab & _
"" & vbTab & " " & quantity & vbTab & rate & vbNewLine)
Loop
Else
MsgBox("Unit rate does not exist", vbCritical, "Bridge Construction Cost Estimate")
End If
It raises the exception when it reaches the do while loop indicating at pay item.

Answer 1

So the specified name does not exist in the DataReader as the documentation suggests:
IndexOutOfRangeException: No column with the specified name was found
and i cannot see this column in your query. You are selecting only quantity and rate.