The number of use cases for subsearches in the real world might be small, but for those situations where they can be applied, subsearches can be a magic bullet. Let's look at an example and then talk about some rules.
Let's start with these events:
2015-02-10 12:59:59 msgid=704783 [email protected] [email protected] 2015-02-10 12:59:59 msgid=171755 [email protected] [email protected] 2015-02-10 12:59:59 msgid=668955 [email protected] [email protected] 2015-02-10 12:59:59 msgid=001404 [email protected] [email protected] 2015-02-10 12:59:59 msgid=284794 [email protected] [email protected] 2015-02-10 12:59:59 msgid=362127 [email protected] [email protected] 2015-02-10 12:59:59 msgid=571419 [email protected] to=ronnie@g&r.com
From these events, let's find out who mary has sent messages to. In these events, we see that the from and to values are in different entries. We could use...