Question

Lately i been doing some work on my MySql class in php and as result of optimizing some parts of my code i would like to narrow some function count down.
I am really having hard time to work with 3 or more tables because it’s getting really confusing there. I don’t have a lot experience working with MySql or any other database, but i know the basics and little bit more.

And for the problem i can’t figure our how to make statement like so:

[table1 – users.email] AND [table2 – subscribers.email] NOT IN [table3 – check.email]

In words that would look like “Get me all unique user emails from [table1] and [table2] that are not in [table3] and put them in 1 list “

By 1 list i mean the same as this statement does it

SELECT u.email FROM users AS u UNION
SELECT s.email FROM subscribers AS s

Thanks in advance, please say if you need any more information.

Answer 1

You left join the 3rd table and then do “where t3.field IS NULL”

example:

SELECT u.email FROM users AS u 
LEFT JOIN table3 t3 ON u.email = t3.email
WHERE t3.email IS NULL
UNION 
SELECT s.email FROM subscribers AS s
LEFT JOIN table3 t3 ON s.email = t3.email
WHERE t3.email IS NULL

You need to make this distinct as well to get unique results.