Efficient SQL query with multiple selects

Question

I'm currently at university and doing a project where I have queries such as:

Select * from recent_purchases where customer_id in 
(  select customer_id from 
   customers where name like '%john%'
) 

I'm not sure if this is the most idiomatic way of doing things or if I'm missing the "correct" way of doing it - it certainly feels a bit clunky. I don't really understand joins yet. Sorry if a stupid question.

Answer 1

Use an INNER JOIN instead of a Sub-Select in the WHERE clause:

Select * 
from recent_purchases rp 
inner join customers c on c.customer_id = rp.customer_id 
where c.name like '%john%'