Access Oracle without tnsnames.ora

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Introduction

Have you ever tried to access an Oracle instance from VBScript? It is not too complicated, but normally you need an additional file called tnsnames.ora in the Oracle installation directory. This article describes an easy way to access an Oracle instance without this file. All you have to do is use a different connection string.

Using the code

You can use this kind of connection strings from VBScript, VBA and Visual Basic. I also tested it with Perl, it worked. Using a connection string without the need to have a correct tnsname.ora on your computer is especially useful for ad hoc scripting on many different database instances, or when you are not sure if the user has a correct tnsnames.ora on his computer.

First take a look at the standard connection string for Oracle, used in a VBScript file:

Dim strCon
strCon = "Driver={Microsoft ODBC for Oracle}; " & _
         "CONNECTSTRING=MYDB; uid=read;pwd=read;"

You see in the first section the driver name (Microsoft ODBC for Oracle), followed by the alias for the instance, and last the Oracle username and password. The alias name MYDB also needs a corresponding entry in the file tnsnames.ora. Mostly you will find this file in the following directory: <Oracle-Home>\network\admin. In this file you need a definition of the alias:

MYDB.WORLD =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = mysrv)(PORT = 7001))
    )
    (CONNECT_DATA =
      (SERVICE_NAME = MYDB)
    )
  )

Oracle uses this definition to determine which physical database instance is associated with the given alias MYDB. This is why we need the file tnsnames.ora when we access an Oracle instance. But is this necessary? No, not really! All you have to change: include the physical connection data (like host and port) in your connection string. Here is the modified connection string in VBScript:

Dim strCon
strCon = "Driver={Microsoft ODBC for Oracle}; " & _
         "CONNECTSTRING=(DESCRIPTION=" & _
         "(ADDRESS=(PROTOCOL=TCP)" & _
         "(HOST=mysrv)(PORT=7001))" & _
         "(CONNECT_DATA=(SERVICE_NAME=MYDB))); uid=read;pwd=read;"

Now you will be able to access every Oracle instance, without the need to have a correct tnsnames.ora on your client machine. Finally here is the complete source code that selects some rows and writes them to STDOUT:

Dim strCon
strCon = "Driver={Microsoft ODBC for Oracle}; " & _
         "CONNECTSTRING=(DESCRIPTION=" & _
         "(ADDRESS=(PROTOCOL=TCP)" & _
         "(HOST=mysrv)(PORT=7001))" & _
         "(CONNECT_DATA=(SERVICE_NAME=MYDB))); uid=read;pwd=read;"

Dim oCon: Set oCon = WScript.CreateObject("ADODB.Connection")
Dim oRs: Set oRs = WScript.CreateObject("ADODB.Recordset")
oCon.Open strCon
Set oRs = oCon.Execute("SELECT myfield FROM mytable)
While Not oRs.EOF
    WSCript.Echo oRs.Fields(0).Value
    oRs.MoveNext
Wend
oCon.Close
Set oRs = Nothing
Set oCon = Nothing

I hope that you find this article useful. For me this kind of a connection string is useful, when I cannot be sure if the end-user had a correct tnsnames.ora on his computer.