I have a table that lists users who have logged in and out of a server. The table lists the PID, which is a number...
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for their ID, an event -- either logged in or logged out, and a timestamp. I threw in a small sample table below... How do I write an SQL statment to display the PID and time the user was logged in to the server?
PID Event TimeStamp 1234 Login 10:00 5678 Login 10:20 1234 Logout 11:30 5678 Logout 11:40
The trick here is to match up each login with its logout. Again, a scalar subquery in the SELECT clause comes to the rescue. But first, let's create and populate our table (note: this is Oracle flavored SQL):
create table ConnectionLog ( PID number(4), Event varchar(6), Logged date ); insert into ConnectionLog values (1234, 'Login', to_date('12-MAR-2002 10:00','DD-MON-YYYY HH24:MI')); insert into ConnectionLog values (5678, 'Login', to_date('12-MAR-2002 10:20','DD-MON-YYYY HH24:MI')); insert into ConnectionLog values (1234, 'Logout', to_date('12-MAR-2002 11:30','DD-MON-YYYY HH24:MI')); insert into ConnectionLog values (5678, 'Logout', to_date('12-MAR-2002 11:40','DD-MON-YYYY HH24:MI'));
select PID, ( ( select min(Logged) from ConnectionLog where PID = t.PID and Logged > t.Logged ) - Logged ) * 24 * 60 as DurationInMinutes from ConnectionLog t where Event = 'Login';
PID DURATIONINMINUTES ---- ----------------- 1234 90 5678 80
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