Question

我想使用vb.net和MySQL作为数据库防止重复输入我的库存表单，这是我的代码：

 Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
    Dim myCommand As New MySqlCommand
    Dim conn As MySqlConnection
    Dim i As String
    conn = New MySqlConnection
    conn.ConnectionString = "server = localhost;username= root;password= a;database= secret"
    Try
        conn.Open()
    Catch mali As MySqlException
        MsgBox("connot establish connection")
    End Try

    Dim intReturn As Integer
    Dim strSql As String = " select * from personnel where pcode = @pcode"

    Dim sqlcmd As New MySqlCommand(strSql, conn)
    With sqlcmd.Parameters
        .AddWithValue("@pcode", CType(pcode.Text, String))
    End With

    intReturn = sqlcmd.ExecuteScalar

    If (intReturn > 0) Then
        cmd = New MySqlCommand("Insert into personnel values('" & pcode.Text & "','" & lname.Text & "','" & fname.Text & "','" & office.Text & "','" & designation.Text & "')")
        i = cmd.ExecuteNonQuery


        If pcode.Text <> "" Then
        ElseIf i > 0 Then
            MsgBox("Save Successfully!", MessageBoxIcon.Information, "Success")
            mrClean()
            ListView1.Tag = ""
            Call objLocker(False)
            Call LVWloader()
            Call calldaw()
        Else
            MsgBox("Save Failed!", MessageBoxIcon.Error, "Error!")
        End If
    Else
        MsgBox("Personnel ID Already Exist!", MessageBoxIcon.Error, "Error!")

    End If

结束子

我在搜索答案时找到了这个，但是当我试图运行它时，它不会读取插入命令，而是直接进入msbox“人员ID已经存在”，即使没有相同的人员ID。< / p>

有人可以检查为什么它不能读取插页，

我的数据库表值：

pcode =主键

lname = longtext

fname = longtext

office = longtext

指定= longtext

任何帮助将不胜感激，谢谢，

Answer 1

很抱歉说这是错误的方法。

数据库具有内置系统以防止数据被复制。这是通过主键或唯一键约束。在您的情况下，您已经创建了一个主键。因此，您无需执行SELECT COUNT(*)查询。

相反，只需直接插入表中并在pcode已存在时捕获完整性错误。

Try
    cmd = New MySqlCommand("Insert into personnel values('" & pcode.Text & "','" & lname.Text & "','" & fname.Text & "','" & office.Text & "','" & designation.Text & "')")

    i = cmd.ExecuteNonQuery


    If pcode.Text <> "" Then
    ElseIf i > 0 Then
        MsgBox("Save Successfully!", MessageBoxIcon.Information, "Success")
        mrClean()
        ListView1.Tag = ""
        Call objLocker(False)
        Call LVWloader()
        Call calldaw()
    Else
        MsgBox("Save Failed!", MessageBoxIcon.Error, "Error!")
    End If
Catch ex As MySqlException
    MsgBox("Personnel ID Already Exist!", MessageBoxIcon.Error, "Error!")
End Try

另请参阅MySQL手册页

Answer 2

应该有你的方式：

1）在插入前写入一个触发器，并检查是否存在任何类似的行 2）在列上放置唯一索引

Answer 3

找到了答案，就像@ e4c5所说的那样，这是一个错误的方法，所以我重新构建了我的代码并最终使其工作，只是想分享答案，也许它会帮助别人。

Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
Dim myCommand As New MySqlCommand
Dim conn As MySqlConnection
Dim i As String
conn = New MySqlConnection
conn.ConnectionString = "server = localhost;username= root;password= a;database= secret"
Try
    conn.Open()
Catch mali As MySqlException
    MsgBox("connot establish connection")
End Try
    Dim retval As String
    Select Button4.Tag
            Case "ADD"
    with myCommand
       .Connection = conn
       .CommandText = "Select pcode from personnel where pcode = '" & pcode.Text & "'"
        retval = .ExecuteScalar
    If retval Is Nothing Then
      .CommandText = "Insert into personnel values ('" & pcode.Text & "','" & lname.Text & "','" & fname.Text & "','" & office.text & "','" & designation.Text & "')"
      .ExecuteNonQuery()
  Else
  MsgBox("Personnel ID Already Exist!", MessageBoxIcon.Error, "Error")
 End If
End With
End Sub

防止重复输入数据库

3 个答案: