在哪裏加載SELECT MAX（id）在vbnet

Question

我有一個問題從表中獲取最後id的值。

由於加載整列會給我一個未來的問題（DataTable有其限制），所以我決定尋找另一種解決方案，但我沒有運氣讓它工作。

我有字符串命令，但我不知道在哪裏存儲返回的值。 這裏是我的代碼：

 Dim query As String = "SELECT MAX(id) AS LastId FROM Table1" 
    Dim dtmain As New DataTable 
    Try 
     With sqlcmd 
      .CommandText = query 
      .Connection = sqlcon 
     End With 

     With sqladp 
      .SelectCommand = sqlcmd 
      .Fill(dtMain) 
     End With 
     MsgBox("last id = " & dtmain.Rows(0)("LastId")) 
    Catch ex As Exception 

    End Try 

我得到什麼和msgbox甚至不會顯示。

注：我想從表中最後一個id和不插入id。

這是我引用和聲明：

Imports System.Data.OleDb 
    Private conn As OleDbConnection 
    Private adapter As OleDbDataAdapter 
    Private cmdd As OleDbCommand 

也是我在我的項目引用添加Microsoft ADO Ext 2.8 for DDL and Security

Answer 1

如果您的數據源是在當前數據庫：

Dim dbConnect As Database 
Dim rstRecordset As DAO.Recordset 

Set dbConnect = Access.CurrentDb 

Dim query As String = "SELECT MAX(id) AS LastId FROM Table1" 

Set rstRecordset = dbConnect .OpenRecordset(query) 
MsgBox("last id = " & rstRecordset.Fields(0).value & "")) 

dbConnect.Close 
Set dbConnect = Nothing 
Set rstRecordset = Nothing 

如果您的數據源在另一個Access數據庫中：

Dim cnnConn As ADODB.connection 
Dim rstRecordset As ADODB.Recordset 
Dim cmdCommand As ADODB.Command 

' Open the connection. 
Set cnnConn = New ADODB.connection 
With cnnConn 
    .ConnectionString = _ 
     "Provider=Microsoft.Jet.OLEDB.4.0" 
    .Properties("Jet OLEDB:Database Password") = "pass" 
    .Open "D:\Databases\Database.mdb" 
End With 

' Set the command text. 
Set cmdCommand = New ADODB.Command 
Set cmdCommand.ActiveConnection = cnnConn 
With cmdCommand 
    .CommandText = "SELECT MAX(id) AS LastId FROM Table1" 
    .CommandType = adCmdText 
    .Execute 
End With 

' Open the recordset. 
Set rstRecordset = New ADODB.Recordset 
Set rstRecordset.ActiveConnection = cnnConn 
rstRecordset.Open cmdCommand 
MsgBox("last id = " & rstRecordset.Fields(0).value & "")) 

' Close the connections and clean up. 
cnnConn.Close 
Set cmdCommand = Nothing 
Set rstRecordset = Nothing 
Set cnnConn = Nothing