How can I restrict that the some ID can only login once in the some time

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I use Login control's Authenticate event to authenticate use.
I find that different users can use the same ID to login in the same time.
How can I restrict that the some ID can only login once in the some time

 

[Charlie@NISH]

Try to keep track of logins in database. On login enter a new record for
person, then on logout, remove record. When a new user logs in, first query
database to see if someone else is currently logged-in using his
credentials.

Charlie

 

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Thanks,
But how can I know a user logout?

Maybe the user press the logout button, or session time out or he close ID
without press the logout button.