This one has stumped me. 

A quick overview
----------------

I need to be able to get all email addresses of people who have participated in a message thread. People can add messages to this messageThread via a few different means, and because people can either be the sender or receive a message, the email addresses might be in different columns. 

Here is an example table.

`messagesTable`

```
ID | threadKey |  fromEmail   |  toEmail    | sentBy   |   sentTo
1  | ASJHD2    | me@exam.com  | you@bob.com |  null    |   null
2  | ASJHD2    | jake@k.com   |             |  null    |   null
3  | ASJHD2    |              |             |  55      |   88

```

I also have my `Users` table. 

```
   ID   | username  | email
   55   | Ike       | ike@domain.com
   88   | Sam       | sam@j.com

```

Now is it possible to get all of the distinct emails that have participated in the message with a threadKey of `ASJHD2`. Keeping in mind that there would also need to be a join on the users table.