Return a Count of 0 When No Rows - sql

Question

OK, I've looked this up and tried a number of solutions, but can't get it to work. I'm a bit of a novice. Here's my original query - how can I get it to return 0 for an account when there are no results in the student table?
SELECT a.NAME
,count(s.student_sid)
FROM account a
JOIN inst i ON a.inst_sid = i.root_inst_sid
JOIN inst_year iy ON i.inst_sid = iy.inst_sid
JOIN student s ON iy.inst_year_sid = s.inst_year_sid
WHERE s.demo = 0
AND s.STATE = 1
AND i.STATE = 1
AND iy.year_sid = 16
AND a.account_sid IN (
20187987
,20188576
,20188755
,52317128
,20189249
)
GROUP BY a.NAME;

Answer 1

Use an outer join, moving the condition on that table into the join:
select a.name, count(s.student_sid)
from account a
join inst i on a.inst_sid = i.root_inst_sid
join inst_year iy on i.inst_sid = iy.inst_sid
left join student s on iy.inst_year_sid = s.inst_year_sid
and s.demo = 0
and s.state = 1
where i.state = 1
and iy.year_sid = 16
and a.account_sid in (20187987, 20188576, 20188755, 52317128, 20189249)
group by a.name;
count() does not count null values, which s.student_sid will be if no rows join from student.

Answer 2

You need to LEFT JOIN and then SUM() over the group where s.student_sid is not null:
select
a.name,
sum(case when s.student_sid is null then 0 else 1 end) as student_count
from account a
join inst i on a.inst_sid = i.root_inst_sid
join inst_year iy on i.inst_sid = iy.inst_sid
left join student s
on iy.inst_year_sid = s.inst_year_sid
and s.demo = 0
and s.state = 1
where i.state = 1
and iy.year_sid = 16
and a.account_sid in (20187987, 20188576, 20188755, 52317128, 20189249)
group by a.name;
This is assuming that all of the fields in the student table that you are filtering on are optional. If you don't want to enforce removal of records where, say, s.state does not equal 1, then you need to move the s.state=1 predicate into the WHERE clauses.
If, for some reason, you are getting duplicate student IDs and students are being counted twice, then you can change the aggregate function to this:
count(distinct s.student_id) as student_count
...which is safe to do as count(distinct ...) ignores null values.