subtract value from database field with update

You need a query string like this:

UPDATE YOURTABLE SET YOURFIELD=YOURFIELD-1 WHERE (SOME CONDITION HERE)

Do you need the vb code portion?

ok can you help me with this

why did this not subtract my value

Dim up As New SqlCommand("UPDATE CHRTR SET REMSEAT = REMSEAT-1 WHERE CourseID=@CourseID", conn)
up.Parameters.Add("@CourseID", Data.SqlDbType.Int).Value = ID
 conn.Open()
cmd.ExecuteNonQuery()

Dim sSQL as String = "UPDATE CHRTR SET REMSEAT = REMSEAT-1 WHERE CourseID=@CourseID"
cmd.CommandText = sSQL
cmd.Parameters.Add("@CourseID", Data.SqlDbType.Int).Value = ID
 conn.Open()
cmd.ExecuteNonQuery()

hmmm, it still did not work

Dim cmd as New SQLCommand
Dim sSQL as String = "UPDATE CHRTR SET REMSEAT = REMSEAT-1 WHERE CourseID=@CourseID"
cmd.Connection = conn
cmd.CommandText = sSQL
cmd.Parameters.Add("@CourseID", Data.SqlDbType.Int).Value = ID
 conn.Open()
cmd.ExecuteNonQuery()

ok here is my code maybe this will help

    Protected Sub RegisterCourse(ByVal sender As Object, ByVal e As RepeaterCommandEventArgs)
        If e.CommandName = "Cancel" Then
            Dim ID As Integer = CType(e.CommandArgument, Integer)
            'Register the course here
            Using conn As New SqlConnection(ConfigurationManager.ConnectionStrings("TCPRODConnectionString3").ConnectionString)
                Dim cmd As New SqlCommand("UPDATE Registrations SET CancelledTime=getdate() WHERE CancelledDate IS NULL AND UserID=@UserID AND CourseID=@CourseID", conn)
                cmd.Parameters.Add("@UserID", Data.SqlDbType.Int).Value = Session("CWID")
                cmd.Parameters.Add("@CourseID", Data.SqlDbType.Int).Value = ID
                Dim sSQL As String = "UPDATE CHRTR SET REMSEAT = REMSEAT-1 WHERE CourseID=@CourseID"
                cmd.CommandText = sSQL
                cmd.Parameters.Add("@CourseID", Data.SqlDbType.Int).Value = ID
                conn.Open()
                cmd.ExecuteNonQuery()
                CourseTable.DataBind()
            End Using
        End If
    End Sub

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ok i do not get an error but it only works when the user cancels a clas from my cancel link how can i make it were it will subtract the class on page load

   Protected Sub RegisterCourse(ByVal sender As Object, ByVal e As RepeaterCommandEventArgs)
        If e.CommandName = "Cancel" Then
            Dim ID As Integer = CType(e.CommandArgument, Integer)
            'Register the course here
            Using conn As New SqlConnection(ConfigurationManager.ConnectionStrings("TCPRODConnectionString3").ConnectionString)
                Dim cmd As New SqlCommand("UPDATE Registrations SET CancelledTime=getdate() WHERE CancelledDate IS NULL AND UserID=@UserID AND CourseID=@CourseID", conn)
                cmd.Parameters.Add("@UserID", Data.SqlDbType.Int).Value = Session("CWID")
                cmd.Parameters.Add("@CourseID", Data.SqlDbType.Int).Value = ID
                conn.Open()
                cmd.ExecuteNonQuery()
                cmd.Parameters.Clear()
                Dim sSQL As String = "UPDATE CHRTR SET REMSEAT = REMSEAT-1 WHERE ID=@CourseID"
                cmd.CommandText = sSQL
                cmd.Parameters.Add("@CourseID", Data.SqlDbType.Int).Value = ID
                cmd.ExecuteNonQuery()
                conn.Close()
                CourseTable.DataBind()
            End Using
        End If
    End Sub

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ok i fixed it thanks for your help

Great answer fast respons works with the user