php - Calculating time difference between events in mysql -

assuming have table following structure :

how calculate time difference between events login , logout specific users? want aggregate of session times each user had(so aggregate of times between each login , logout sessions). aware datediff can used i'm not sure syntax , how able use multiple users

the final out put :

+-------------+-------------------------+ | agent       | total session time      | +-------------+-------------------------+ | user - 194  | 00:30:00                | | user - 195  | 00:40:00                | +-------------+-------------------------+ 

my version outputs difference between last logout , login actions:

select t1.agent, timediff(t2.lot, t1.lit)  (select agent, max(time) lit        log event = 'login' group 1) t1    join (select agent, max(time) lot          log event = 'logout' group 1) t2    on t1.agent = t2.agent  group 1; 

i used following table definition:

create table `log` (   `time` datetime default null,   `agent` varchar(50) default null,   `event` enum('login','logout') default null ) 

example data , output

data:

+---------------------+-------+--------+ | time                | agent | event  | +---------------------+-------+--------+ | 2015-07-23 15:40:18 | u1    | login  | | 2015-07-23 14:40:24 | u2    | login  | | 2015-07-23 16:40:34 | u1    | logout | | 2015-07-23 16:40:39 | u2    | logout | | 2015-07-23 16:44:19 | u2    | login  | | 2015-07-23 16:46:25 | u2    | logout | +---------------------+-------+--------+ 

result of select:

+-------+--------------------------+ | agent | timediff(t2.lot, t1.lit) | +-------+--------------------------+ | u1    | 01:00:16                 | | u2    | 00:02:06                 | +-------+--------------------------+