Question

I am wondering if anyone can explain to me when you would use a sub query and when you would use a join.

for example.

I have this query:

SELECT * from contacts where id in (select contactId from contactgrouplink where groupId = 1);

What would the benefit be of a join over this sub query?

Answer 1

select * from contacts x, contactgrouplink y where x.id=y.contactId and y.groupId=1

Use EXPLAIN just before each of those query’s… to see what query does!