Question

我想检查Access数据库中是否已存在条目。通过我的研究，我成功地为此获得了一些代码，但它给了我一些错误。你能指出我正确的方向来实现我想要的代码。

这是我的代码：

Dim commandText = "SELECT COUNT(*) AS FROM ESRRegister WHERE ID = '" & IDtxt.Text & "'"
    Using (conn = New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\Database\Database.accdb"))
        Using ("select = New OleDbCommand(commandText, conn)")
            conn.open()
            Dim count = Convert.ToInt32("select.ExecuteScalar()")
            If count > 0 Then
                MessageBox.Show("Already Exists!", "ALI ENTERPRISES", MessageBoxButtons.OK, MessageBoxIcon.Information)
            Else 'Your insert code cmd.CommandText = "insert into ESRRegister (Dt,ID)VALUES ('" & Dttxt.Text & "' , '" & IDtxt.Text & "')" queryResult = cmd.ExecuteScalar() MsgBox("Added Successfuly") 
            End If
        End Using
    End Using

如果您对代码提供一些解释，那将是很棒的，bcoz我是.NET的新手

非常感谢

Answer 1

'The SQL instruction as a string
commandText = "SELECT COUNT(*) AS FROM ESRRegister WHERE ID = '" & IDtxt.Text & "'"
'Open the connection to the Database
Connection.Open()
    'Use the SQLinstruction to create an OleDBcommand
    Dim mySQLCommand As System.Data.OleDb.OleDbCommand = New System.Data.OleDb.OleDbCommand(commandText, Connection)
    'Perform the SQL-instruction
    Dim count as integer = CInt(mySQLCommand.ExecuteScalar)
    mySQLCommand.Dispose() 'Clean the command object
Connection.Close() 'Close/Clean connection

Answer 2

Dim commandText As String = "SELECT NZ(COUNT(*),0) FROM ESRRegister WHERE ID = '" & IDtxt.Text & "'"
Using conn as New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\Database\Database.accdb")
dim Cmd As New OleDbCommand(commandText, conn
    conn.open()
    Dim count as intiger = Convert.ToInt32(Cmd.ExecuteScalar())
    If count > 0 Then
        MessageBox.Show("Already Exists!", "ALI ENTERPRISES", MessageBoxButtons.OK, MessageBoxIcon.Information)
    Else
        cmd.CommandText = "insert into ESRRegister (Dt,ID)VALUES ('" & Dttxt.Text & "' , '" & IDtxt.Text & "')" 
        Dim queryResult as Variant = cmd.ExecuteNonQueryr() 
        MsgBox("Added Successfuly") 
    End If
End Using

select是VB.net中保存的单词，我将OleDbCommand的名称更改为Cmd

检查从.NET访问是否存在重复条目

2 个答案: