How To Use GUIDs w/ Access, SQL 6.5 and SQL 7

MORE INFORMATION

The following files are available for download from the Microsoft Download Center:
Release Date: DEC-29-1998

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base: Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file.

   FileName                  Size
   ---------------------------------------------------------

   AdoGUID.bas                 3KB
   AdoGUID.exe                60KB
   AdoGUID.frm                25KB
   AdoGUID.frx                 1KB
   AdoGUID.mdb                80KB
   AdoGUID.vbp                 2KB
   Readme.txt                  4KB

				

Microsoft Access has a ReplicationID AutoNumber field that is a 16-byte (128 bit) Globally Unique Identifier (GUID) that uniquely identifies each record in the database. Please reference the sample project for the code that demonstrates how to SELECT specific GUIDs and Insert GUIDs using the AutoNumber field with Microsoft Access. The following function is a code snippet from the sample that demonstrates how to SELECT a specific GUID from an Access table using Microsoft ActiveX Data Objects (ADO):

Sample Code

   Sub AccessReQueryADO()

   On Error GoTo ErrorMessage

   Dim adoCn As adoDb.Connection
   Dim adoRs As adoDb.Recordset
   Dim strCn As String
   Dim strSQL As String

   strCn = App.Path & "\adoGUID.mdb"

   Set adoCn = New adoDb.Connection
   With adoCn
       .Provider = "Microsoft.JET.OLEDB.3.51"
       .CommandTimeout = 500
       .ConnectionTimeout = 500
       .Open strCn, "admin", ""
   End With

   If Option7.Value = True Then
       strSQL = "SELECT * FROM GUIDtable WHERE " & _
                "Instr(1,[colGUID],'" & strGUID & "')"
   Else
       strSQL = "SELECT * FROM GUIDtable"
   End If

   Set adoRs = New adoDb.Recordset
   With adoRs
       Set .ActiveConnection = adoCn
       .LockType = adLockOptimistic
       .CursorLocation = adUseServer
       .CursorType = adOpenForwardOnly
   End With

   adoRs.Open strSQL

   txtMessage.Text = ""

   While Not adoRs.EOF
       txtMessage.Text = txtMessage.Text & _
                         adoRs.Fields("colGUID").Value & "  |  "
       txtMessage.Text = txtMessage.Text & _
                         adoRs.Fields("colDescription").Value & vbCrLf
       adoRs.MoveNext
   Wend

   GoTo ExitSub

   ErrorMessage:
       MsgBox Err.Number & " : " & vbCrLf & Err.Description

   ExitSub:
       Label6.Caption = "- ReQueried AccessADO GUID Table..."
       Set adoCn = Nothing
       Set adoRs = Nothing

   End Sub
				

Unlike SQL 6.5, SQL 7.0 supports a GUID datatype known as UNIQUEIDENTIFIER. This datatype is a 16-byte GUID stored in the same format as the Microsoft Access AutoNumber (GUID) datatype. There are subtle differences concerning how to Insert and Retrieve the GUIDs among the different database engines. Since SQL 6.5 does not support a native GUID datatype the methods used for storing/retrieving GUIDs are much different than SQL 7.0 or Microsoft Access. SQL 7.0 with the OLEDB provider is almost the same as Microsoft Access with or without the OLEDB provider (SQLOLEDB), as you will see in the sample code. With SQL 6.5 you must store the GUID as a VarBinary(16) datatype. Consequently, to retrieve the GUID with SQL65 you must use a stored procedure and build a Command object with the appropriate ByteArray parameter to pass to the stored procedure SELECT statement.

NOTE: You must use the same code techniques with SQL 7.0 as with SQL 6.5 if you are using the ODBC provider (MSDASQL) since in ODBC 3.51 and below the GUID datatype is not recognized.
The 16-byte (128 bit) data structure of a GUID:

   typedef struct _GUID
   {
       unsigned long        Data1;
       unsigned short       Data2;
       unsigned short       Data3;
       unsigned char        Data4[8];
   } GUID;
				

   * Data1
   An unsigned long integer data value.
   * Data2
   An unsigned short integer data value.
   * Data3
   An unsigned short integer data value.
   * Data4
   An array of unsigned characters.
				

To demonstrate GUIDs with SQL 7.0 or SQL 6.5 in the sample project you must specify a valid (test) SQL 7.0/SQL 6.5 server and database. To do so, navigate to the Connection Info tab and change the Server and Database reference. The defaults are (local) Server and the Pubs database. Also, to use the native GUID datatype for SQL 7.0, you must change to the OLEDB provider (SQLOLEDB) by clicking the appropriate option button in the Provider frame at the top of the Form. If you select ODBC as the provider for SQL 7.0 then the application uses the same code as with SQL 6.5.

NOTE: The Connection Info tab has no bearing on Microsoft Access. The default database for Microsoft Access is included with the sample project AadoGUID.mdb as should reside in the Application path.

For each database you select in the sample project you must run Create Table to create the GUID test table and then Insert to automatically generate some test GUID data before running a ReQuery.

NOTE: CoCreateGUID() is called in the Insert sample code to generate the test GUID values.

In the sample application there is a ByteArray2GUID() function that is used to convert the VarBinary(16) byte array to a GUID string for display. Also, the function is used to convert the GUID string to a byte array for storage in the SQLServer VarBinary(16) datatype column. Note that the function is needed when using the GUIDs interchangeably between Microsoft Access and SQL 6.5. If you Export the Microsoft Access table to SQL 6.5 you will see that the bytes are not stored in the same order in which they display in the Microsoft Access table view. For example:

     Reversed...        Not Reversed...
   >----------------<|>---------------<
   20C68F83-9593-0011-BFBB-00C04F8F8347 'SQLServer view after table Export.
   838FC620-9395-1100-BFBB-00C04F8F8347 'Microsoft Access view.
				

NOTE: The bytes are in (DWord and Word) reverse order after Exporting the Microsoft Access table.

Because the Microsoft Access Upsizing Wizard results in the same storage of the bytes in SQL 6.5, you must use the ByteArray2GUID() and GUID2ByteArray() functions to remain compatible with the storage of the GUIDs in Microsoft Access. If you do not need to Export the Microsoft Access table to SQL 6.5 or upsize the Microsoft Access database to SQL 6.5 then you need only store the bytes in a straightforward fashion.

The following is a code snippet from the code sample that demonstrates the storage of the GUID in the byte format of Microsoft Access.

Sample Code

   Sub SQL65InsertGUID()

   'Insert GUID record.
   On Error GoTo ErrorMessage

   Dim adoCn As adoDb.Connection
   Dim adoRs As adoDb.Recordset
   Dim strGUIDtmp As String
   Dim bytGUID() As Byte
   Dim strCn As String
   Dim strSQL As String

   strCn = "Provider=" & strProvider & _
           ";Driver={SQL Server}" & _
           ";Server=" & txtServer & _
           ";Database=" & txtDatabase & _
           ";Uid=" & txtUserID & _
           ";Pwd=" & txtPassword

   Set adoCn = New adoDb.Connection
   With adoCn
       .ConnectionString = strCn
       .CommandTimeout = 500
       .ConnectionTimeout = 500
       .Open
   End With

   strGUIDtmp = strGUID

   bytGUID = GUID2ByteArray(FilterGUID(strGUIDtmp))

   strSQL = "SELECT * FROM GUIDtable WHERE 1=0"

   Set adoRs = New adoDb.Recordset
   With adoRs
      Set .ActiveConnection = adoCn
      .LockType = adLockOptimistic
      .CursorLocation = adUseServer
      .CursorType = adOpenForwardOnly
   End With

   adoRs.Open strSQL

   adoRs.AddNew
   adoRs.Fields("colGUID").Value = bytGUID
   adoRs.Fields("colDescription").Value = "This is a test GUID"
   adoRs.Update

   GoTo ExitSub

   ErrorMessage:
      MsgBox Err.Number & " : " & vbCrLf & Err.Description

   ExitSub:
      Label6.Caption = "[ASCII 176] Inserted SQL65 GUID Record..."
      Set adoCn = Nothing
      Set adoRs = Nothing

   End Sub

   '======================
   Function GUID2ByteArray(ByVal strGUID As String) As Byte()

   Dim i As Integer
   Dim j As Integer
   Dim sPos As Integer
   Dim OffSet As Integer
   Dim sGUID(0 To 2) As Byte
   Dim bytArray() As Byte

   ReDim bytArray(0 To 15) As Byte

   sGUID(0) = 7
   sGUID(1) = 11
   sGUID(2) = 15

   OffSet = 0
   sPos = 0

   'AABBCCDD-AABB-CCDD-XXXX-XXXXXXXXXXXX 'Microsoft Access view.
   'DDCCBBAA-BBAA-DDCC-XXXX-XXXXXXXXXXXX 'SQLServer view.
   'Need to loop through to build the GUID byte array in the Microsoft
   'Access storage format since the first eight bytes are reversed.
   For i = 0 To UBound(sGUID)
      For j = sGUID(i) To (OffSet + 1) Step -2
         bytArray(sPos) = "&H" & Mid$(strGUID, j, 2)
         sPos = sPos + 1
      Next j
      OffSet = sGUID(i)
   Next i

   For i = 17 To 31 Step 2
      bytArray(sPos) = "&H" & Mid$(strGUID, i, 2)
      sPos = sPos + 1
   Next i

   GUID2ByteArray = bytArray()

   End Function