How to get selected cell values of last row from SQL database into two labels? - vb.net

Question

I am trying to get values from selected columns of the last row into label 1 and label 2 when the form is loaded from a SQL database. My code is not working. How can I do this?
My code is here:
Private Sub getvalue()
Dim strConn = "server= PANKAJ\SQLEXPRESS; database = pankaj billing software; integrated security=true"
Dim sqlConn = New SqlConnection(strConn)
sqlConn.Open()
Dim sqlcmd As New SqlCommand("select 22ktrate, 21ktrate from ratedata where max(rateid) = #rateid", sqlConn)
Dim myreader As SqlDataReader
myreader = sqlcmd.ExecuteReader()
myreader.Read()
If myreader.HasRows Then
Label1.Text = myreader.Item("22ktrate")
Label2.Text = myreader.Item("21ktrate")
End If
sqlConn.Close()
End Sub

Answer 1

The big thing I noticed is nothing sets the #rateid parameter.
Private Sub getvalue()
Dim conn As String = "server= PANKAJ\SQLEXPRESS; database = pankaj billing software; integrated security=true"
Dim sql As String = "select [22ktrate], [21ktrate] from ratedata where max(rateid) = #rateid"
Using sqlConn As New SqlConnection(conn), _
sqlcmd As New SqlCommand(sql, sqlConn)
'This was missing. You need to know what to set for 1234 here.
'I suggest adding it as argument to the method.
sqlcmd.Parameters.Add("#rateid", SqldbType.Int).Value = 1234
sqlConn.Open()
Using myreader As SqlDataReader = sqlcmd.ExecuteReader()
If myreader.Read() Then
Label1.Text = myreader("22ktrate").ToString()
Label2.Text = myreader("21ktrate").ToString()
End If
End Using
End Using
End Sub
I made other structural changes to the code, too, and you should follow this new pattern. The original code in the question had several less-noticeable issues that could eventually cause user-facing issues, such as failing to close the connection if an exception was thrown.
Finally, I saw this in the comments:
i just want last row two selected column values from sql database
There is no ORDER BY clause in that select statement. Without an ORDER BY clause, the order for the rows is undefined and Sql Server is free to give you the rows in any order it finds convenient. There is no meaningful definition for "last row". If this matters, you must add an ORDER BY clause to the sql statement... at which point, you are better off inverting the order and only taking the first record, rather than iterating the entire result set. If it doesn't matter... you're still better of just taking the first row vs iterating the entire set. In either case, you could also add a TOP 1 to the SQL command — if it's even possible to have more than one record match the max(rateid).

Answer 2

Actually, I can see that you're already using the reader to check if it had rows.
Just set the last value AFTER the reader has read.
This assumes that the Order by of your SQL query is correct (asc or desc)
Change this part:
myreader = sqlcmd.ExecuteReader()
myreader.Read()
If myreader.HasRows Then
Label1.Text = myreader.Item("22ktrate")
Label2.Text = myreader.Item("21ktrate")
End If
sqlConn.Close()
to
While myreader.Read()
Label1.Text = myreader.Item("22ktrate")
Label2.Text = myreader.Item("21ktrate")
End While
sqlConn.Close()