Question

I have an MS Access program in use in multiple locations. It connects to MS SQL Server tables, but the server name is different in each location. I am looking for the fastest way to test for the existence of a server. The code I am currently using looks like this:

ShellWait "sc \\" & ServerName & " qdescription MSSQLSERVER > " & Qt(fn)
FNum = FreeFile()
Open fn For Input As #FNum
Line Input #FNum, Result
Close #FNum
Kill fn

If InStr(Result, "SUCCESS") Then ...

ShellWait: executes a shell command and waits for it to finish
Qt: wraps a string in double quotes
fn: temporary filename variable

I run the above code against a list of server names (of which only one is normally available). The code takes about one second if the server is available and takes about 8 seconds for each server that is unavailable. I’d like to get both of these lower, if possible, but especially the fail case as this one happens most often.

Answer 1

The solution I eventually settled on was to use nslookup.exe as a precursor to my sc.exe command. If the SQL Server server does not exist, nslookup tells me so immediately. Making this change cut down the time it took to fail on a SQL Server lookup from about 8 seconds to well under 1 second. The success case is actually slightly longer, but not noticeable. For those who may be interested, here is my final solution (hopefully the purpose of my personal functions [ShellWait, Qt, PassThru, LogError] will be obvious):

UPDATE: I’ve updated the function to incorporate dmaruca’s clsRunApp (my new favorite class module) and the issue raised by Philippe concerning working in disconnected mode. The result is much better than I originally posted and I’d like to thank both of them for their contributions. Here’s the function as it stands now:

Function SQLServerDBExists(ComputerName As String, DbName As String) As Boolean
Const LocalHost = "127.0.0.1"
Dim Result As String, RunApp As New clsRunApp

    On Error GoTo Err_SQLServerDBExists

    If ComputerName <> LocalHost And _
       ComputerName <> "." And _
       ComputerName <> Environ("COMPUTERNAME") Then
        'Check for existence of the server using Name Server Lookup'
        Result = RunApp.RunAppWait_CaptureOutput("nslookup " & ComputerName)
        If InStr(Result, "Non-existent domain") Or _
           InStr(Result, "Default servers are not available") Then
            SQLServerDBExists = False
            GoTo Exit_SQLServerDBExists
        End If
    End If

    Result = RunApp.RunAppWait_CaptureOutput("sc \\" & ComputerName & " qdescription MSSQLSERVER")
    If InStr(Result, "SUCCESS") Then
        With PassThru("SELECT Name FROM sysdatabases " & _
                      "WHERE Name='" & DbName & "'", "master", ComputerName)
            SQLServerDBExists = (Not .EOF)
        End With
    End If

Exit_SQLServerDBExists:
    Exit Function
Err_SQLServerDBExists:
    LogError Err.Number, Err.Description, "SQLServerDBExists", "AttachToSQL"
    Resume Exit_SQLServerDBExists
End Function

Note: I realize Environ(“COMPUTERNAME”) is not a 100% reliable way of determining the computer’s name, so feel free to replace that with your own code if you want. I think the lazy approach is sufficient for its purpose here.