查询AND条件即使在错误的参数上也返回true

Question

以下查询返回1，即使我提供了错误的用户名，它只是比较密码为什么？

conn.ConnectionString=ConfigurationManager.ConnectionStrings("CoreConnection").ConnectionString
conn.Open()

cmd = New OleDbCommand("Select count(1) from admin where userid=@userid and password=@password", conn)
cmd.Parameters.AddWithValue("@userid", TextBox1.Text)
cmd.Parameters.AddWithValue("@password", TextBox2.Text)
Dim result As Integer = cmd.ExecuteScalar

conn.Close()

If (result > 0) Then
    'MessageBox.Show("Success")
    ad.Show()
Else
    MsgBox("Invalid username or Password!")
End If