How can I insert a value in a specified column together with the other columns without appearing it into a new another row alone?

Question

I am creating a login logout system for our College Library that records the students\' time in and time out whenever they enter or exit in our library.

I am using VS 20

Answer 1

You need to use UPDATE, not INSERT. Assuming they are not able to log out unless they have logged in (i.e. there is record in tblCollegeStudentLog where StudentTimeIn is NULL, you can just use:

UPDATE  tblCollegeStudentLog
SET     StudentTimeOut = @OutTime
WHERE   StudentNumber = @StudentNumber
AND     StudentTimeOut IS NULL;

Then you would use SqlParameters to properly execute the command and not leave yourself vunerable to SqlInjection, poor SQL Plan caching and data type issues:

Dim Sql as String = "UPDATE tblCollegeStudentLog SET StudentTimeOut = @OutTime WHERE StudentNumber = @StudentNumber AND StudentTimeOut IS NULL;"
Using cmd = New SqlCommand(Sql, con)
    cmd.Parameters.AddWithValue("@OutTime", Convert.ToDateTime(lblTimeOutNya.Text))
    cmd.Parameters.AddWithValue("@StudentNumber", lvwLog.SelectedItems(0).Text)
    con.Open()
    If cmd.ExecuteNonQuery() = 0 Then
        'If no rows are affected then there was not a valid
        'record to update, i.e. the student was not logged in
        MsgBox("You were not logged in")
    Else
        MsgBox("You are now logged out!")
    End If
End Using

N.B. Please excuse my VB.NET, I have not used it in quite some time so there may be some syntax errors.