When should I use cross apply over inner join?

Question

What is the main purpose of using CROSS APPLY?

I have read (vaguely, through posts on the Internet) that cross apply can be more efficient when selectin

Answer 1

Cross apply can be used to replace subquery's where you need a column of the subquery

subquery

select * from person p where
p.companyId in(select c.companyId from company c where c.companyname like '%yyy%')

here i won't be able to select the columns of company table so, using cross apply

select P.*,T.CompanyName
from Person p
cross apply (
    select *
    from Company C
    where p.companyid = c.companyId and c.CompanyName like '%yyy%'
) T