Access提供了能够从SQL查询中调用用户定义的VBA函数，但该功能仅限于由Microsoft Access应用程序本身内的制作的查询。这是因为VBA函数需要执行Access应用程序的基础结构（特别是VBA表达式服务）。

在你的情况下，你可能能够运行在你的C＃代码中使用 Microsoft.Office.Interop.Access 实现 Access 查询，但这会给你一个 DAO Recordset 对象，摆弄这个与 OleDbDataAdapter 一起工作的东西可能比它的价值更麻烦（如果可能的话）。

您可能***在C＃中重新创建VBA函数逻辑。

I have written an ms-access function in a module called ‘StripLead’. I made a single line procedure called ‘CallFunction’. Now when I call this procedure from ms-access it works fine. But when I call this procedure from C# I get error:

Undefined function 'Striplead' in expression.

Ms-access module code:

Public Function StripLead(pstrPhrase As String) As String
  Dim strFirstWord As String
  Dim strReturn As String
  Dim intPos As Integer

  strReturn = pstrPhrase
  intPos = InStr(pstrPhrase, " ")
  If intPos > 0 Then
    strFirstWord = Left$(pstrPhrase, intPos - 1)
    Select Case strFirstWord
      Case "A", "An", "The"
      strReturn = Right$(pstrPhrase, Len(pstrPhrase) - intPos)
    End Select
  End If

StripLead = strReturn
End Function

Ms-access procedure "CallFunction"(sql view):

SELECT Customers.ID, Striplead([ContactName]) AS a FROM Customers;

C# code:

   public void CallStoredProcedure(string NewQry)
       {
           try
           {
            DataTable tbl = new DataTable();
            using (OleDbConnection connection = new OleDbConnection(ConnectionString))
            {
                OleDbCommand cmd = new OleDbCommand();
                cmd.CommandText = "CallFunction";
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Connection = connection;

                using (OleDbDataAdapter adp = new OleDbDataAdapter(cmd))
                {
                    adp.Fill(tbl);
                }
            }

         }
        catch(Exception ex)
        {
            throw;   
        }
    }

Please suggest whether the approach is incorrect. Or else, if there is a way to make call to ms-access function from C# to fetch data. My aim is to fetch modified data from ms-access and fill the datagrid in C#.

Access offers the ability to call user-defined VBA functions from SQL queries, but that capability is restricted to queries that are made from within the Microsoft Access application itself. That is because the VBA functions require the Access application's infrastructure (specifically, the VBA "Expression Service") to execute.

In your case you might be able to run a "real" Access query from within your C# code using Microsoft.Office.Interop.Access but that would give you a DAO Recordset object, and fiddling around with that to work with an OleDbDataAdapter could well be more trouble than it's worth (if it is possible at all).

You'll probably just be better off to re-create the VBA function logic in C#.