VB.NET SQL Server:必须声明标量变量

Question

我正在尝试创建一个从数据库中删除用户的查询。但当我确认删除用户时，它会给我一个错误：

System.Data.SqlClient.SqlException(0x80131904(：必须声明标量变量"@Username"。

Imports System.Data.SqlClient
Public Class DeleteForm
Private Sub btnDelete_Click(sender As Object, e As EventArgs) Handles btnDelete.Click
Dim RetVal As Integer
Dim conn = New SqlConnection("Data Source=(localdb)MSSQLLocalDB;Initial Catalog=dbProject;Integrated Security=True")
Using cmd = New SqlCommand("select count(*) from tblLogin where username = @Username and password = @Password", conn)
cmd.Parameters.Add("@Username", SqlDbType.VarChar).Value = txtUsername.Text
cmd.Parameters.Add("@Password", SqlDbType.VarChar).Value = txtPassword.Text
conn.Open()
If conn.State = ConnectionState.Open Then
RetVal = CInt(cmd.ExecuteScalar)
If RetVal = 1 Then
If txtPassword.Text And txtCheckPassword.Text <> "" Then
If txtCheckPassword.Text = txtPassword.Text Then
Dim cancConf As Integer = MessageBox.Show("This cant be undone!" & vbCrLf & "Are you sure?", "Warning!", MessageBoxButtons.YesNo, MessageBoxIcon.Warning)
If cancConf = DialogResult.Yes Then
Try
Dim queryDelete As String = "DELETE FROM tblLogin WHERE username = @Username"
Dim cmdDelete As New SqlClient.SqlCommand(queryCancellazione, conn)
cmdCancellazione.ExecuteNonQuery()
MsgBox("Account deleted succesfully!")
cmdCancellazione.Dispose()
conn.Close()
LoginForm.Show()
Me.Close()
Catch ex As Exception
MsgBox(ex.ToString())
End Try
ElseIf cancConf = DialogResult.No Then
End If
Else
MsgBox("The passwords arent matching!", MsgBoxStyle.Exclamation)
End If
ElseIf txtPUtenteCANC.Text <> "" And txtPUtenteCONF.Text = "" Then
MsgBox("Please, confirm the password")
End If
Else
MsgBox("User not found!", MsgBoxStyle.Exclamation)
txtNUtenteCANC.Clear()
txtPUtenteCANC.Clear()
txtPUtenteCONF.Clear()
txtNUtenteCANC.Select()
End If
Else
MessageBox.Show("The connection is not open!" & vbCrLf & "The program will close", "Warning!", MessageBoxButtons.OK, MessageBoxIcon.Error)
End
End If
End Using
End Sub
End Class

Answer 1

您已将该参数添加到SELECT COUNT命令中，但没有添加到DELETE命令中。

Dim queryCancellazione As String = "DELETE FROM tblLogin WHERE username = @Username"
Dim cmdCancellazione As New SqlClient.SqlCommand(queryCancellazione, conn)
cmdCancellazione.Parameters.Add("@Username", SqlDbType.VarChar).Value = txtUsername.Text