Question

I have an email subscription table and a user table. I need to combine the two to get all the emails, since it’s possible to create an account without subscribing and vice versa. Easy enough so far:

SELECT email FROM emailcapture
UNION
SELECT email FROM cpnc_User

Now, this gets me the complete list of all emails. For each email on this combined list, I need to add an extra piece of information: the created date. Both emailcapture and cpnc_User tables have a “created” field. The created date should be the earlier of the two dates, if both dates exist, or, if only one exists and the other is NULL, it should just be the one that exists.

How can I change this query so that it returns this extra piece of information, the created date? Keep in mind that the new query I seek should return exactly the same number of rows as the query above.

Thanks,
Jonah

Answer 1

SELECT i.email, MIN(i.date_creation) FROM
(SELECT email, date_creation FROM emailcapture
UNION ALL
SELECT email, date_creation FROM cpnc_User) as InnerTable i
GROUP BY i.email