What's wrong in this TSQL query?

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    Literal1.Text = Request.QueryString("Pno")
    On Error Resume Next
    Dim SQLData As New System.Data.SqlClient.SqlConnection("workstation id=ws.example.com;packet size=4096;user id=some-user;pwd=some-password;data source=mssql.example.com;persist security info=False;initial catalog=some-db")
    Dim cmdSelect As New System.Data.SqlClient.SqlCommand("SELECT * FROM a1_ticket WHERE PNR_no ='" & Literal1.Text & "'", SQLData)
    SQLData.Open()
    Dim dtrReader As System.Data.SqlClient.SqlDataReader = cmdSelect.ExecuteReader()
    If dtrReader.HasRows Then
        While dtrReader.Read()
            Literal2.Text = dtrReader("bus_type")
            Literal3.Text = dtrReader("dep_time")
            Literal4.Text = dtrReader("PRN")
            Literal5.Text = dtrReader("fro_m")
            Literal6.Text = dtrReader("seat_opt")
            Literal7.Text = dtrReader("Ticket_no")
            Literal8.Text = dtrReader("t_o")
            Literal9.Text = dtrReader("taxes")
            Literal10.Text = dtrReader("Travels")
            Literal11.Text = dtrReader("journey_date")
            Literal12.Text = dtrReader("net_pay")
            Literal13.Text = dtrReader("name")
    开发者_开发百科        Literal14.Text = dtrReader("seat_opt")
            Literal15.Text = dtrReader("sel_seat")
            Literal16.Text = dtrReader("bd_point")
        End While
    Else
    End If
    Dim cmd As New System.Data.SqlClient.SqlCommand("SELECT * FROM a1_vendors WHERE UserId ='" & Request.QueryString("tid") & "'", SQLData)
    cmd.ExecuteScalar()
    Literal17.Text = dtrReader("travels")
    Literal18.Text = dtrReader("Contactno")
    SQLData.Close()
    dtrReader.Close()
    SQLData.Close()
End Sub

What's wrong with this query? It's begging for a SQL injection attack.

See:

Dim cmd As New SqlCommand(
   "SELECT * FROM a1_vendors WHERE UserId ='" & 
   Request.QueryString("tid") & "'", SQLData)

What if Request.QueryString("tid") contained the value "'' GO DROP TABLE a1_vendors GO SELEC ''"

Suddenly your command becomes "SELECT * FROM a1_vendors WHERE UserId = '' GO DROP TABLE a1_vendors GO SELECT ''"

I expect you mean the second one, where you SELECT * but ExecuteScalar; ExecuteScalar only returns one value (as the result) - and it doesn't update a reader, so Literal17 / Literal18 are getting their values from nowhere.

Following your existing pattern, it should be something like:

' caveat: this is **not** intended as a perfect example; this intentionally
' uses the same pattern as the question; see below for notes
dtrReader = cmd.ExecuteReader()
If dtrReader.Read()
    Literal17.Text = dtrReader("travels")
    Literal18.Text = dtrReader("Contactno")
End If

more importantly, though

• no separation; everything from connection-string management, account credentials (thanks for those, btw), data access and UI is handled right there in a Page_Load event, itself the cause of great gnashing of teeth
• susceptible to SQL injection
• no using (or the VB equivalent) to make sure you have deterministic cleanup, rather than waiting on garbage collection (in the inevitable event of exceptions)