从数据库中读取字段

Public Function GetUserFirstName(UserName As String) As String
    Dim Firstname As String = ""
    
    'Specify the SQL that you want to use including a Parameter
    Dim SQL As String = "select firstname from users where username=@UserName"
    
    'Provide a Data Source
    Dim DBDSN As String = "Data Source=server.address;Initial Catalog=DatabaseName;Persist Security Info=True;User ID=UserName;Password=UserPassword"

    Dim dbConn As New SqlConnection(DBDSN)

    Dim dbCommand As New SqlCommand(SQL, dbConn)

    'Provide one or more Parameters
    dbCommand.Parameters.AddWithValue("@UserName", UserName)

    'An optional Timeout
    dbCommand.CommandTimeout = 600

    Dim reader As SqlDataReader
    Dim previousConnectionState As ConnectionState = dbConn.State
    Try
        If dbConn.State = ConnectionState.Closed Then
            dbConn.Open()
        End If
        reader = dbCommand.ExecuteReader
        Using reader
            With reader
                If .HasRows Then
                    'Read the 1st Record
                    reader.Read()
                    'Read required field/s
                    Firstname = .Item("FirstName").ToString
                End If

            End With

        End Using

    Catch
        'Handle the error here
    Finally
        If previousConnectionState = ConnectionState.Closed Then
            dbConn.Close()
        End If
        dbConn.Dispose()
        dbCommand.Dispose()

    End Try
    'Pass the data back from the function
    Return Firstname

End Function

使用上述功能很简单：

   Dim UserFirstName as string=GetUserFirstName(UserName)