Loop SQL if has Rows then continue - sql

Question

I am trying to run this loop to run if the results continue to have rows. So basically if my sql statement continues to return a row on ssql = "SELECT TOP 1 * from [OrderHeader] Where ([IsisDownloadDate] is null or [IsisDownloadDate] = '')"
then run submit to webrequest, then return a value, then submit that value to the same row and update that column
So basically I just want it to keep updating the next row as long as ssql keeps returning rows, and if it does not return any rows then stop.
I got everything to work, besides the continuous looping issue
Here is the code:
Private Sub Button5_Click(sender As Object, e As EventArgs) Handles Button5.Click
Dim objDR As SqlClient.SqlDataReader
Dim objCommand As SqlClient.SqlCommand
Dim ConnectionString As String = "Data Source=localhost;Initial Catalog=datarep;user id=sa;password=test123;"
Dim objConnection As SqlClient.SqlConnection
Dim ssql As String
objConnection = New SqlClient.SqlConnection(ConnectionString)
ssql = "SELECT TOP 1 * from [OrderHeader] Where ([IsisDownloadDate] is null or [IsisDownloadDate] = '')"
If objConnection.State <> ConnectionState.Open Then
objConnection.Open()
End If
objCommand = New SqlClient.SqlCommand(ssql, objConnection)
objDR = objCommand.ExecuteReader(CommandBehavior.CloseConnection)
objCommand = Nothing
If objDR.HasRows Then
While objDR.Read()
Dim objSO As New WebReference.SalesOrder
Dim objBTAddr As New WebReference.BillToAddress
Dim objSTaddr As New WebReference.ShipToAddress
Dim objAddr As New WebReference.Address
Dim objPart() As WebReference.SalesOrderPart
Dim objMisc As New WebReference.SalesOrderMiscCharges
Dim objPayment As New WebReference.Payment
Dim objCreditCard As New WebReference.SalesOrderCreditCard
Dim objApproval As New WebReference.SalesOrderCreditCardApproval
objSO.OrderNumber = "69355522"
objSO.CompanyId = "301"
objSO.CustomerNumber = "5838303"
objSO.Code = "I"
objSO.PONumber = objDR("OrderNumber").ToString()
objSO.Source = "TAW.COM"
objSO.OrderDate = Format(Date.Now, "MM/dd/yy")
objSO.RequiredDate = Format(Date.Now, "MM/dd/yy")
objSO.ShipCode = "UPG"
objSO.EmployeeId = "1"
objAddr.Name = "José Peña,EPS H-1607"
objAddr.Address1 = "LÄRKGATAN 9"
objAddr.City = "Québec"
objAddr.Country = "US"
objAddr.State = "CA"
objAddr.Zip = "90220"
objSTaddr.Address = objAddr
'objSTaddr.Phone = "310-900-5509"
objBTAddr.AccountNumber = "595522"
objBTAddr.Address = objAddr
objSO.BillToAddress = objBTAddr
'turn on for .88
'objSO.ShipTo = objSTaddr
'objSO.ShipTo.Phone = objSTaddr.Phone
ReDim objPart(1)
objPart(0) = New WebReference.SalesOrderPart
objPart(0).PartNumber = "EVE510-621"
objPart(0).PartId = "EVE"
objPart(0).Quantity = 1
objPart(0).Price = 39.99
objPart(0).Description = "PWRAID SPCR"
objSO.Parts = objPart
Dim ws As New WebReference.WebServiceTyped
Dim result As WebReference.SubmitOrder = ws.SubmitSalesOrder(objSO)
Dim ordernum As String = result.OrderId
Dim s As String = "Data Source=localhost;Initial Catalog=datarep;user id=sa;password=test123;"
Dim sql As String
Dim con As New SqlConnection
con = New SqlConnection(s)
con.Open()
sql = "WITH UpdateList_view AS ( SELECT TOP 1 * from [OrderHeader] Where ([IsisDownloadDate] is null or [IsisDownloadDate] = '') ) update UpdateList_view set [IsisDownloadDate] = '" & result.OrderId & "'"
Dim cmd As New SqlClient.SqlCommand(sql, con)
cmd.ExecuteNonQuery()
con.Close()
End While
End If
objDR.Close()
objDR = Nothing
End Sub

Answer 1

Besides the whole, why would you want to do it this way issue, the problem is that you are only selecting one row. Your while loop goes through that singular row then exits. There are a lot of issues with this code though and I would recommend that you do not do it this way.
Let's go through the code a little bit. Let's say there are two rows that fit this criteria, row J and row 6. You select top 1 and you get row J back. Your If objDR.HasRows will evaluate to true and you will go into the while condition. After you read and update, you go back to the while condition. You already read row J and your vb.net code is not aware of what else is in the database, so we exit the while loop and exit the sub.
I recommend selecting all the rows that fit your criteria right off the bat. Selecting all of your data instead of top 1 will be better than selecting what you want one row at a time from the database because it is expensive to go out and connect to the database. Your way, you will be connecting to the database twice for each row that fits the criteria. My way, you will connect once for each row plus one more time at the beginning. If you are updating a lot of rows this will be a huge difference. Your sql should look more like
SELECT UniqueId from [OrderHeader] Where ([IsisDownloadDate] is null or [IsisDownloadDate] = '')
Now when you loop, you are going through all of the data. I also recommend that when you update the data make sure you use a parameter that will update the specific row you are looking at, some sort of unique id is usually best. In reality, you don't need a cte for this either. Something like:
sql = New SqlCommand("UPDATE UpdateList_view SET [IsisDownloadDate] = #OrderId WHERE UniqueId = #ID", dbConn)
sql.Parameters.AddWithValue("#OrderId", result.OrderId)
sql.Parameters.AddWithValue("#Id", objDR.GetInt32(0))
Note, objDR.GetInt32(0) would be setting the #Id parameter to the unique id that would be selected in the first sql query. Also, please please look at how I have added parameters to the sqlCommand. You should get into the habit of coding this way because update UpdateList_view set [IsisDownloadDate] = '" & result.OrderId & "'" leaves you open to sql injection.
Lastly, you may want to consider doing a sql bulk update rather than updating each row one at a time. This is probably a good place to start.