SqlDataReader getting rows when no data

Question

Hi!

This is incredibly urgent, I need to present this application in 3 and a half hours.

My application checks against a data source to see if a value exists in the database and changes values depending on whether or not the value in question was found. The problem is that I've run the sql query with the value in question in SSMS and no rows were returned, and yet, my DataReader says it has rows.

This means that my application is reporting inaccurately. Here's my code:

Using conn As New SqlConnection("Data Source=.\SQLEXPRESS; Initial Catalog=Testing;       Integrated Security=True;")
    Dim cmd As New SqlCommand(sql, conn)

    conn.Open()
    Dim reader As SqlDataReader = cmd.ExecuteReader

    If reader.HasRows Then
       Value = True
       AcctNumber = reader(1)
    End If

    reader.Close()
End Using

I've removed code that's not relevant to this post, but what you may want to know is:

Value is Boolean AcctNumber is a String

As this is an application for work, I'd rather not include the SQL Query. The problem is the reader. If I comment out Value = True, I get the right info, but leaving that out will mean that in a case where Value should be True, it'll report inaccurately as well.

Thanks in advance!

EDIT: Full Source Code:

Case "Business"
    ' Change the number format to local because that's what it is in the db
    If Microsoft.VisualBasic.Left(NumberToCheck, 2) = "27" Then
        NumberToCheck = NumberToCheck.Replace(Microsoft.VisualBasic.Left(NumberToCheck, 2), "0")
    End If

    Dim sql As String = "SELECT a.TelNumber, c.AccountNumber " & _
            "FROM TelInfo a " & _
            "INNER JOIN Customers b ON a.CustID = b.pkguidId " & _
            "INNER JOIN Accounts c ON b.pkguidId = c.CustID " & _
            "WHERE a.TelNumber = '" & NumberToCheck & "'"
    Using conn As New SqlConnection("Data Source=.\SQLEXPRESS; Initial Catalog=Testing; Persist Security Info=True; " & _
        "User Id=JoeSoap; Password=paoseoj;")
        Dim cmd As New SqlCommand(sql, conn)

        conn.Open()
        Dim reader As SqlDataReader = cmd.ExecuteReader

        If reader.Read Then
            Value = True
            AcctNumber = reader(1)
         End If

        reader.Close()
    End Using

On the comments below made before 08/02/10 (mm/dd/yy):

Value is just a boolean that gets returned by the function to indicate that the searched telephone number (NumberToCheck) exists in the database.

So...

Private AcctNumber As String

Dim val As Boolean = False
val = CheckNumber("3235553469")
If val Then
    ' AcctNumber will have been set by CheckNumber
    Label1.Text = AcctNumber
End If

val will only be returned True if the NumberToCheck (in this example 3235553469) exists in the database.

Having copied the value of NumberToCheck into SSMS and testing the query there, I can verify that the query does work as expected.

No, I can't populate a DataSet because of the volume of information in the table (+/- 9.5m rows). Even with the 'WHERE' filter, the query is too heavy on resources and eventually ends in an OutOfMemory Exception which is why I went with a DataReader.

I'm going to try the ExecuteScalar option as suggested as an answer by Darryl now, will update with the results.

Answer 1

Try changing your If statement to

If reader.Read() Then
   Value = True
   AcctNumber = reader(1)  
End If

HasRows exhibits strange behavior in certain situations, so it's better to avoid it altogether.

Answer 2

Just to be sure it's not a data problem, parameterize your SQL. Change the statement:

Dim sql As String = "SELECT a.TelNumber, c.AccountNumber " & _
        "FROM TelInfo a " & _
        "INNER JOIN Customers b ON a.CustID = b.pkguidId " & _
        "INNER JOIN Accounts c ON b.pkguidId = c.CustID " & _
        "WHERE a.TelNumber = @telNumber"

Then do this:

Dim cmd As New SqlCommand(sql, conn)
cmd.Parameters.AddWithValue("@telNumber", NumberToCheck) ' <==== added line

Edit

I think we're looking in the wrong place. Add this just before if reader.Read():

Value = false
AcctNumber = ""

This will make sure you're not having a variable-scope problem. (You are using Option Strict On, right?)

Answer 3

This does not solve the problem, but it may get you through your presentation. Use "ExecuteScalar" which should work when you return a single value.

    AcctNumber = ""
    AcctNumber = cmd.ExecuteScalar
    If AcctNumber = "" Then
        Value = False
    Else
        Value = True
    End If

Answer 4

In the immortal words of Homer Simpson... "DOH!!"

I just had a look on the database that my application searches for the telephone numbers and, I don't know how I could have missed it, but the value I'm searching for is actually there.

The problem is, therefore, not likely anything to do with my code, but rather the data...