Return maximum ID number from a database - sql

Question

This is probably an easy thing to do, but I'm only doing my first vb project so I'm not sure how to do this 100%, so apologies in advanced if the following problem is actually very simple.
Basically, what I need to do is, when loading a database table into an ultragrid, I need to retrieve the maximum integer that is stored in a field.
To explain this more clearly, each record in the database has it's own ID number, so I need to iterate each record and find the one with the highest ID number, and return the ID, so that this can then be used in other calculations.
I know that I can use SQL = SELECT MAX(supportID) FROM tblIncidents for example to retrieve the highest ID number stored in this table.
So, how do I go about declaring the result of this (so, the highest ID number) as variable so that I can firstly display it in a messagebox to prove to me that the query has worked, and secondly so that I can use the variable as means of using the ID throughout my code?
An example; This is the code to save a new record into the tblIncidents table.
Private Sub btnSave_Click(sender As Object, e As EventArgs) Handles btnSave.Click
Dim incidentSolved As Boolean = False
If cboxSolved.Checked Then
incidentSolved = True
End If
If txtClientSave.Text = "" Then
MsgBox("Client name cannot be blank")
ElseIf rtbProblem.Text = "" Then
MsgBox("Problem cannot be blank")
ElseIf cboxSolved.Checked = True And rtbSolution.Text = "" Then
MsgBox("Please enter solution")
Else
database.SaveNewIncident(txtClientSave.Text, dtpStart.Value, dtpEnd.Value, rtbProblem.Text, dtpStartTime.Value, dtpEndTime.Value, cboxSolved.Checked, rtbSolution.Text, _con)
txtClientSave.Text = ""
rtbProblem.Text = ""
rtbSolution.Text = ""
dtpStart.Value = Date.Today
dtpEnd.Value = Date.Today
dtpStartTime.Value = DateTime.Now
dtpEndTime.Value = DateTime.Now
cboxSolved.Checked = False
End If
End Sub
Database function that is called
Public Shared Function SaveNewIncident(ByVal clientName As String, dateStart As Date, dateEnd As Date, ByVal incidentProblem As String, ByVal timeStart As String, ByVal timeEnd As String,
ByVal incidentSolved As Boolean, ByVal incidentSolution As String, _Con As OleDbConnection)
Dim tr As OleDbTransaction = Nothing
Try
tr = _Con.BeginTransaction()
Dim Dc As New OleDbCommand
Dc.Connection = _Con
Dc.CommandType = CommandType.Text
Dc.CommandText = "INSERT INTO dbo.tblIncidents VALUES(?, ?, ?, ?, ?, ?, ?, ?, ?)"
Dc.Transaction = tr
Dc.Parameters.Add("#clientName", OleDbType.VarChar).Value = clientName
Dc.Parameters.Add("#dateStart", OleDbType.Date).Value = dateStart
Dc.Parameters.Add("#dateEnd", OleDbType.Date).Value = dateEnd
Dc.Parameters.Add("#incidentProblem", OleDbType.LongVarChar).Value = incidentProblem
Dc.Parameters.Add("#timeStart", OleDbType.VarChar).Value = timeStart
Dc.Parameters.Add("#timeEnd", OleDbType.VarChar).Value = timeEnd
Dc.Parameters.Add("#incidentSolved", OleDbType.Boolean).Value = incidentSolved
Dc.Parameters.Add("#incidentSolution", OleDbType.LongVarChar).Value = incidentSolution
Dc.ExecuteNonQuery()
tr.Commit()
MsgBox("Save successful")
Catch ex As Exception
mdInit.errorLog(ex.Message, ex.StackTrace)
MsgBox("Failed to save data, refer to error log")
tr.Rollback()
End Try
End Function

Answer 1

what you can do in VB.net is define a SQLcommand which will require a SQL connection attached to it - since your query returns a single value you will be able to execute it with ExecuteScalar to return a single value eg
Dim cmd AS New SqlClient.SQLCommand("SELECT MAX(billID) FROM tblRecurring",connectionString)
then
cmd.connection.open
and then
dim x as MaxId = cmd.executeScalar
and finish off with
cmd.connection.dispose
of course