Negativ tilstand i Join

Du har mange måder at bruge left join with is null eller not exists

Select 
un.user_id 
from user_notifications un
left join user_push_notifications upn 
on upn. user_id = un.user_id  and un.notification_id  = 'xxxxyyyyyzzzz' 
where upn. user_id is null

Select 
un.user_id 
from user_notifications un
where 
un.notification_id  = 'xxxxyyyyyzzzz' 
and not exists
(
 select 1 from user_push_notifications upn 
 where 
 un.user_id = upn.user_id 
 and upn.notification_id = 'xxxxyyyyyzzzz'
)

For at øge ydeevnen skal du muligvis tilføje indeks, hvis det ikke er tilføjet endnu

alter table user_notifications add index user_notifi_idx(user_id,notification_id);
alter table user_push_notifications add index user_notifp_idx(user_id,notification_id);