+---------+-----------+--------+
| user_id | email     | action |
+---------+-----------+--------+
| 1       | aa@aa.com | open   |
+---------+-----------+--------+
| 2       | null      | click  |
+---------+-----------+--------+
| 3       | ac@ac.com | click  |
+---------+-----------+--------+
| 4       | ad@ad.com | open   |
+---------+-----------+--------+

+---------+-----------+--------+
| user_id | email     | event  |
+---------+-----------+--------+
| 1       | aa@aa.com | sent   |
+---------+-----------+--------+
| 1       | ab@aa.com | none   |
+---------+-----------+--------+
| null    | ac@ac.com | none   |
+---------+-----------+--------+
| 2       | ad@ab.com | sent   |
+---------+-----------+--------+
| 4       | ad@ad.com | sent   |
+---------+-----------+--------+