I'm asking this as a more general question on which will perform better. I'm trying to get a set of comments and their score/rankings from two tables.
comments
cid (integer, primary key)
title
body
comment_ratings
cid (integer, primary key)
uid (integer, primary key)
score
Option 1 (Single group by query)
select c.cid,c.title,c.body,coalsece(sum(r.score),0) as score
from comments c left outer join comment_ratings r on c.cid = r.cid
group by c.cid,c.title,c.body;
Option 2 (Two simple queries)
select cid,title,body from comments;
select cid,sum(score) from comment_ratings;
I know that in general you always want to keep the number of queries to a minimum and that Option 1 is the most logical/preferred way to proceed. However, I've greatly simplified Option 1. In practice I'm going to be pulling a lot more columns and will be inner joining to additional tables. So my real question is whether having a lot of items in the group by clause will have an adverse effect on performance.
Thanks in advance,
Jonathon
