使用多个where子句选择多个查询

Question

I have two select queries I want to combine for faster performance. I'm a bit confused as I'm not sure if I could use a JOIN or LEFT JOIN or something else to make it faster.

Here are the two queries I want to combine:

Query 1:

SELECT id FROM users WHERE email = :email LIMIT 1

Then, if that row exists from query 1, then run query 2:

SELECT * FROM settings WHERE id = :id_from_query_1

thank you for any kind of help!

Answer 1

When making a join query you can specify what column to join on. In this case it would be:

select users.id, settings.*
from users
join settings on users.id = settings.id

You could also use a double from clause which I think results in the same speed background wise that would look like:

select users.id, settings.*
from users, settings
where users.id = settings.id

If proper indexes are set a join should be faster than 2 selects. Ofcourse there are many factors when it comes to speed like load, network, what is cached and what isn't etc.