join - MySQL - Correct approach event counting -

i want list users have particular event count i'm confused on approach take.

this database table:

create table `event` (   `event_id` int(11) unsigned not null auto_increment,   `visitor_id` int(11) default null,   `key` varchar(200) default null,   `value` text,   `label` varchar(200) default '',   `datetime` datetime default null,   primary key (`event_id`) ) engine=innodb auto_increment=6 default charset=utf8;   insert `event` (`event_id`, `visitor_id`, `key`, `value`, `label`, `datetime`) values     (1, 1, 'login', null, '', null),     (2, 2, 'login', null, '', null),     (3, 1, 'view_page', 'hotel', '', null),     (4, 2, 'view_page', 'hotel', '', null),     (5, 1, 'purchase_hotel', null, '', null);  create table `visitor` (   `visitor_id` int(11) unsigned not null auto_increment,   `datetime` datetime default null,   primary key (`visitor_id`) ) engine=innodb auto_increment=6 default charset=utf8;  insert `visitor` (`visitor_id`, `datetime`) values     (1, null),     (2, null); 

and approach:

select distinct     t1.`visitor_id`     `visitor` t1  join `event` t2 on t1.visitor_id = t2.visitor_id , t2.`key` = 'login' join `event` t3 on t1.visitor_id = t3.visitor_id , t3.`key` = 'view_page' , t3.`value` = 'hotel' ( select count(*) `event` `event`.`key` = 'purchase_hotel' ) > 0 

this should list visitor 1 list visitor 2 not have purchase_hotel event.

as can imagine, there more "rules" join events each particular case. can correct , improve somehow?

bonus: name of approach?

i think "set-within-sets" query. using aggregation having clause type of query. following checks 3 conditions looking for:

select visitor_id event e group visitor_id having sum(e.key = 'login') > 0 ,        sum(e.key = 'view_page' , e.value = 'hotel') > 0 ,        sum(e.key = 'purchase_hotel') > 0; 

the first condition in having clause counts number of login records , true when @ least 1 found. (if want one, change > 0 = 0.)

the second condition checks viewing of hotel page.

the third counts number of hotel purchases.