Question

当我输入数据时尚未提供。按钮不起作用但是当我在数据库中输入现有数据时，该按钮用于查找数据库和msgbox.appear中的现有记录这是我的编码。（我使用的是Microsoft Visual Basic 2008快速版数据库mysql）

Imports MySql.Data.MySqlClient
Public Class Form2
    Public conn As MySqlConnection
    Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Application.DoEvents()
        Button1.Focus()

        conn = New MySqlConnection
        'conn.ConnectionString = "server=localhost;database=ilmu;userid=root;password= ''"
        Try
            conn.Open()
        Catch ex As Exception
            MessageBox.Show("Error1: " & ex.Message)
        End Try
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        conn = New MySqlConnection("server=localhost;database=ilmu;userid=root;password= ''")
        Try
            conn.Open()
            Dim sqlquery As String = "SELECT * FROM visitor WHERE nama = '" & TextBox1.Text & "';"
            Dim data As MySqlDataReader
            Dim adapter As New MySqlDataAdapter
            Dim command As New MySqlCommand
            command.CommandText = sqlquery
            command.Connection = conn
            adapter.SelectCommand = command
            data = command.ExecuteReader
            While data.Read()
                If data.HasRows() = True Then
                    If data(2).ToString = TextBox2.Text Then
                        command = New MySqlCommand
                        command.Connection = conn
                        tkhupd = Now.ToString("yyyy-MM-dd HH:mm:tt")
                        command.CommandText = "INSERT INTO visitor(noK,khupd)VALUES ('" & TextBox1.Text & "','" & tkhupd & "')"
                        command.ExecuteNonQuery()
                        MessageBox.Show(" Berjaya, Sila Masuk. ", "Tahniah", MessageBoxButtons.OK, MessageBoxIcon.Information)

                    Else
                        MsgBox("exist")

                    End If
                Else
                    MsgBox("Failed Login.")
                End If
            End While

        Catch ex As Exception

        End Try
    End Sub
End Class

Answer 1

我不确定当数据库中没有匹配的记录时你想要做什么，但是没有任何代码会在没有匹配条目的情况下被击中。

如果没有匹配的记录，则不满足您的while条件，并且循环中不会发生任何事情。

修复它可能涉及重新排列循环的顺序和if条件。

检查data.hasRows是否优先。

示例：

If data.HasRows() = True Then
   While Data.Read
       //code here for found rows
   End While
 Else
    //code for no matching entries
 End If

正如Joel的评论中所提到的，你真的应该看看使用参数化查询。

更改了插入命令的示例：

 command.CommandText = "INSERT INTO visitor(noK,khupd)VALUES (?noK,?khupd)"
 command.Parameters.AddWithValue("?noK",TextBox1.Text)
 command.Parameters.AddWithValue("?khupd", tkhupd)
 command.ExecuteNonQuery()

我插入新数据时按钮不起作用

1 个答案: