Query string not retrieving data values - asp.net

Question

Hope you guys could give me some help.
I have a asp.net web form which gets data from SQL database and displays it on webpage via product code number or product description.
Searching by description will display a list of similar products where each list will have a button with the product code when clicked will open another site with extra product information,
e.g.
13892
14589
17485
00010
08890
The problem is all the codes that start from 1 upwards will show more details, but when I click on product codes that start with 0 such as 00010, 08890 will show no data when in fact there should be data.
Any help would be appreciated.
code I have below,
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Val(Request.QueryString("Stock_code")) <> 0 Then
Dim dt As DataTable = New DataTable
Dim strQuery As String = "SELECT STKCODE as [Stock_Code], STKNAME as [Stock_Description], STK_BASEPRICE as [Retail_Price], STK_SORT_KEY2 as [Pack_Size], STK_NOTES as [Notes], STK_P_WEIGHT as [Net_Weight], STK_S_WEIGHT as [Gross_Weight] FROM dbo.STK_STOCK WHERE STKCODE = '" & Val(Request.QueryString("Stock_code")) & "'"
Dim strQUery2 As String = "SELECT LOC_CODE as [Location_Code], LOC_NAME as [Location], LOC_PHYSICAL as [Physical_Stock] FROM dbo.STK_LOCATION WHERE LOC_CODE IN ('WH01','WH03','WH04','WH08','WH11')" & _
"AND LOC_STOCK_CODE = '" & Val(Request.QueryString("Stock_code")) & "'"
Dim strQuery3 As String = "SELECT STKLANG_STOCKNAME as [Chinese_Description] FROM dbo.STK_STOCK_LANG WHERE STKLANG_STOCKCODE ='" & Val(Request.QueryString("stock_code")) & "'"
Dim strQuery4 = "SELECT STK_SELLPRICE1 as [Retail_Price], STK_SELLPRICE5 as [Retail_Rest_Split] FROM dbo.STK_STOCK_2 WHERE STKCODE2 = '" & Val(Request.QueryString("stock_code")) & "'"
Using cmd4 As SqlCommand = New SqlCommand(strQuery4)
Dim da3 As SqlDataAdapter = New SqlDataAdapter
Dim dt4 As New DataTable
cmd4.Connection = cnn : cnn.Open()
da3.SelectCommand = cmd4
da3.Fill(dt4)
For i = 0 To dt4.Rows.Count - 1
Label8.Text = dt4.Rows(i).Item("Retail_Rest_Split")
Next
End Using
cnn.Close()
Using cmd As SqlCommand = New SqlCommand(strQuery)
Dim sda As SqlDataAdapter = New SqlDataAdapter
cmd.Connection = cnn : cnn.Open()
sda.SelectCommand = cmd
sda.Fill(dt)
For i = 0 To dt.Rows.Count - 1
Label7.Text = dt.Rows(i).Item("Stock_Code")
Label1.Text = dt.Rows(i).Item("Notes")
Label3.Text = dt.Rows(i).Item("Retail_Price")
Label4.Text = dt.Rows(i).Item("Pack_Size")
Label5.Text = dt.Rows(i).Item("Stock_Description")
'Label8.Text = dt.Rows(i).Item("Pack_Size")
Label9.Text = dt.Rows(i).Item("Net_Weight")
Label10.Text = dt.Rows(i).Item("Gross_Weight")
GridView1.DataSource = dt
GridView1.DataBind()
Next
End Using
cnn.Close()
Dim dt3 As DataTable = New DataTable
Using cmd3 As SqlCommand = New SqlCommand(strQuery3)
Dim da2 As SqlDataAdapter = New SqlDataAdapter
cmd3.Connection = cnn : cnn.Open()
da2.SelectCommand = cmd3
da2.Fill(dt3)
End Using
For i = 0 To dt3.Rows.Count - 1
Label6.Text = dt3.Rows(i).Item("Chinese_Description")
Next
Dim cmd2 As New SqlCommand
Dim dt2 As New DataTable
Dim da As New SqlDataAdapter
With cmd2
.Connection = cnn
.CommandText = strQUery2
End With
da.SelectCommand = cmd2
da.Fill(dt2)
GridView1.DataSource = dt2
GridView1.DataBind()
End If
End Sub

Answer 1

You want to use a paramaterized query like this (I'm going to fold that query string to make it more readable without having to scroll horizontally):
Dim strQuery As String = "SELECT STKCODE as [Stock_Code], STKNAME as [Stock_Description],
STK_BASEPRICE as [Retail_Price], STK_SORT_KEY2 as
[Pack_Size], STK_NOTES as [Notes], STK_P_WEIGHT as
[Net_Weight], STK_S_WEIGHT as [Gross_Weight] FROM
dbo.STK_STOCK WHERE STKCODE = #StockCode"
Using cmd As New SqlCommand(strQuery)
cmd.Parameters.AddWithValue("#StockCode", Request.QueryString("Stock_code"))
' Do your other stuff here.
End Using
Note, that you don't want to just use string concatenation to insert your query parameter. That opens you up to SQL injection attacks.
Instead, you use a placeholder in your query like #StockCode. Then you call AddWithValue on the command to give it the value of that parameter.
You can also explicitly specify the parameter type if you need to:
' Add CustomerID parameter for WHERE clause.
command.Parameters.Add("#ID", SqlDbType.Int)
command.Parameters("#ID").Value = customerID

Answer 2

Assuming they are all 5 digit codes, this will make sure the stock code is numeric.
Replace
Val(Request.QueryString("Stock_code"))
with
String.Format("{0:00000}", Integer.Parse(Request.QueryString("Stock_code")))
Will raise an exception if Request.QueryString("Stock_code") is not parsed as integer, which prevents against malicious injection.
For example:
Dim stockCode = String.Format("{0:00000}", Integer.Parse(Request.QueryString("Stock_code")))
Dim strQuery As String = "SELECT STKCODE as [Stock_Code], STKNAME as [Stock_Description], STK_BASEPRICE as [Retail_Price], STK_SORT_KEY2 as [Pack_Size], STK_NOTES as [Notes], STK_P_WEIGHT as [Net_Weight], STK_S_WEIGHT as [Gross_Weight] FROM dbo.STK_STOCK WHERE STKCODE = '" & stockCode & "'"
Dim strQUery2 As String = "SELECT LOC_CODE as [Location_Code], LOC_NAME as [Location], LOC_PHYSICAL as [Physical_Stock] FROM dbo.STK_LOCATION WHERE LOC_CODE IN ('WH01','WH03','WH04','WH08','WH11')" & "AND LOC_STOCK_CODE = '" & stockCode & "'"
Dim strQuery3 As String = "SELECT STKLANG_STOCKNAME as [Chinese_Description] FROM dbo.STK_STOCK_LANG WHERE STKLANG_STOCKCODE ='" & stockCode & "'"
Dim strQuery4 = "SELECT STK_SELLPRICE1 as [Retail_Price], STK_SELLPRICE5 as [Retail_Rest_Split] FROM dbo.STK_STOCK_2 WHERE STKCODE2 = '" & stockCode & "'"
#dwilliss has just answered the question using parameters, which is probably better than my method. Posting this anyway