Question

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    | [e-mail]  | [e-mail] |  null    |   null
2  | ASJHD2    | [e-mail]   |             |  null    |   null
3  | ASJHD2    |              |             |  55      |   88

I also have my Users table.

   ID   | username  | email
   55   | Ike       | [e-mail]
   88   | Sam       | [e-mail]

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.

Answer 1

First try to get just emails like

SELECT fromEmail
FROM messagesTable
WHERE fromEmail IS NOT NULL
UNION
SELECT toEmail
FROM messagesTable
WHERE toEmail IS NOT NULL