Mysql 当列匹配值并且不存在时将行复制到另一个表

Question

I'm a long time lurker but my first post, thanks for the invaluable advice over the years!

I have a bit of a mysql conundrum, I'm designing a form for a venue for uses with WiFi and COVID etc, other stuff.

Now, it's a PHP form which writes into a database, the info is kept for 30 days until it's purged (30 days from the date stamp). This runs on an event, every day (and works fine).

I wanted to add in a checkbox to say add them to a mailing list so I figured I needed another table to copy the info for the subscribers that obviously doesn't get purged for use later.

Currently I have this query that works:

INSERT INTO table2
    SELECT *
    FROM table1
    WHERE mailing = 'on';

But I really need to copy the row where mailing='on' AND the email address doesn't exist. It's this part that I'm really stuck on, is it possible to do this within the same query?

Thanks in advance.

Answer 1

You need in something like

INSERT INTO table2 ( {columns list} )
SELECT {columns list}
FROM table1 t1
WHERE mailing='on'
  AND NOT EXISTS ( SELECT NULL
                   FROM table2 t2
                   WHERE t1.email = t2.email );