Excel sheet export to Access via ADODB inconsistent behavior - excel

Question

I am experiencing an odd behavior when I'm exporting an Excel spreadsheet into a Access database via ADODB. The Office version is 2013 32bit running on Win7 64bit. These are the steps:
I have created a new Access file called 'test.accdb' with just one table 'orders' and one field 'OrderID'. The table is empty.
I have created a new .csv file, orders.csv. Later I show the content of this file and the end result.
I have an Excel addin with the following macro:
Public Sub updateAccess()
Dim con As New ADODB.Connection
Dim connectionString As String
Dim rs As New ADODB.Recordset
Dim sql As String
Dim Filename As String
Filename = Application.ActiveWorkbook.Path & "\test.accdb"
connectionString = "Driver={Microsoft Access Driver (*.mdb, *.accdb)};DBQ=" & Filename
connectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" & Filename
Call con.Open(connectionString)
sql = "DELETE FROM orders"
Call con.Execute(sql)
sql = "INSERT INTO orders " & _
"SELECT * FROM [Excel 12.0 Xml;HDR=YES;DATABASE=" & _
ActiveWorkbook.FullName & "].[" & ActiveWorkbook.Sheets(1).Name & "$]"
Set rs = con.Execute(sql)
Call con.Close
Set con = Nothing
End Sub
I then open the order.csv file using Excel, run the macro and then open test.accdb using Access. Depending on the content of the csv file, different results are output:
Case A
orders.csv:
OrderID
1
A
test.accdb, in table 'orders':
OrderID
1
A
Case B
orders.csv:
OrderID
1
A
3
test.accdb, in table 'orders'
OrderID
<blank>
1
3
Case C
orders.csv:
OrderID
1
A
3
B
C
D
test.accdb, in table 'orders'
OrderID
1
3
A
B
C
D
Why is case B failing?
I can't wrap my head around it. I tried two drivers, but no luck.

Answer 1

ADODB with an Excel database will guess the field types from the first 16 records. In the case
OrderID
1
A
3
it will guess numeric field type since numeric is in majority.
To avoid this, you can use the IMEX parameter within the connection string, see: https://www.connectionstrings.com/excel/
So with your code:
...
sql = "INSERT INTO orders " & _
"SELECT * FROM [Excel 12.0 Xml;HDR=YES;IMEX=1;DATABASE=" & _
ActiveWorkbook.FullName & "].[" & ActiveWorkbook.Sheets(1).Name & "$]"
Set rs = con.Execute(sql)
...