Howw to delete session data

hi friends i had a serious issue for my project actualy as u all know
whenever we login a entry is added in the sessions tableof our database
and it re3amins there till we log off

but in case the user clicks the close icon nof the browser (eg, IE or
mozilla )then in that case the session entry reamins intact

my issue was to delete the entry in either case whether the browser is
closed or the user logs off

or to delete the entry when the user types the url again, the session
entry should get regenerated

if u have the solution to my query plz do help me and mail me at
[email protected]

i am eagerly waiting ur reply