query a database and add entry if entry not already present

Question

I would like to add a way to see if an entry is already in a connected database in the following code and if it is, not to add the entry and pop up a dialog saying something to the effect of "already been scanned" and if it is not to proceed as usual. a simple if statement should do.

            Using connection As New SqlClient.SqlConnection("Data Source=XXXXX;Initial Catalog=XXXXXX;Integrated Security=True;Pooling=False;Encrypt=False"), _
    cmd As New SqlClient.SqlCommand("INSERT INTO [XXXXX] (TrackingNumber, Date) SELECT @TrackingNumber, @Date WHERE NOT EXISTS (SELECT * FROM([XXXXX])WHERE TrackingNumber = @TrackingNumber AND Date = @Date)", connection)
        cmd.Parameters.Add("@TrackingNumber", SqlDbType.VarChar, 50).Value = TrNum
        cmd.Parameters.Add("@Date", SqlDbType.DateTime, 8).Value = TrDate
        connection.Open()
        cmd.ExecuteNonQuery()
        connection.Close()
    End Using

Answer 1

You should be able to put your inputs into a subquery that checks for redundancy:

INSERT INTO [XXXXXXX] (TrackingNumber, Date) 
    SELECT @TrackingNumber, @Date from DUAL 
    WHERE NOT EXISTS (
        SELECT * 
        FROM [XXXXXXX]
        WHERE TrackingNumber = @TrackingNumber AND Date = @Date)

Answer 2

My VB.NET might be somewhat off but hopefully this should give the general idea!

Dim rowsAffected AS Integer

    Using connection As New SqlClient.SqlConnection("Data Source=XXXXX;Initial Catalog=XXXXXX;Integrated Security=True;Pooling=False;Encrypt=False"), _
        cmd As New SqlClient.SqlCommand("INSERT INTO [XXXXX] (TrackingNumber, Date) SELECT @TrackingNumber, @Date WHERE NOT EXISTS (SELECT * FROM [XXXXX] WHERE TrackingNumber = @TrackingNumber)", connection)
        cmd.Parameters.Add("@TrackingNumber", SqlDbType.VarChar, 50).Value = TrNum
        cmd.Parameters.Add("@Date", SqlDbType.DateTime, 8).Value = TrDate
        connection.Open()
        rowsAffected = cmd.ExecuteNonQuery()
        connection.Close()
    End Using


If rowsAffected = 0 Then
MsgBox "Scanned Already"
Else
MsgBox "Inserted Succesfully"
End If