Question

I have a person table with fields id, email.

And a subscription table with fields: person_id, category_id.

If a person is subscribed subscription table will have at-least one entry in the table.

I want to query person table with the 3rd column having 1 or 0 depending on whether person is subscribed or not.

select p.id, p.email , [is_subscribed] 
from person p

is_subscribed should be 1 if there is an entry in the subscription table else should be 0.

How can I achieve the above ?

Answer 1

Using a LEFT JOIN on subscription & a count (in a case of several subscriptions)

SELECT p.id,p.email,IF(COUNT(s.category_id)>0,1,0) as is_subscribed
FROM
person as p
LEFT JOIN subscription as s ON s.person_id=p.id
GROUP BY p.id