Question

I have 3 tables users(name, email), reviews(review, entity, user) and votes(vote, entity, user), I want to make a query which returns all the reviews given for a particular entity, and vote from votes table if the user have voted for that entity, else null should be there at the place of vote. The query I wrote is

select users.name as name, 
reviews.review as review, 
votes.vote as vote 
from 
users join reviews on users.email=reviews.user 
left join votes on users.email=votes.user 
where reviews.entity='entity_id'

But this query is resulting multiple rows for some reviews,
I made it working using group by, by am unable to understand the behavior of left join,

Answer 1

You are not joining votes for any specific entity, try the following:

select users.name as name, 
reviews.review as review, 
votes.vote as vote 
from 
users join reviews on users.email=reviews.user 
left join votes on users.email=votes.user and reviews.entity = votes.entity
where reviews.entity='entity_id'