MySQL limit most recent year and use JOIN - mysql

Question

I have the following code and I would like to select only the most recent record (hence why I have written max(a.fiscal_year) except the query returns every fiscal year. How can I adjust the following query to return only the most recent (maximum) fiscal year.
SELECT count(*), b.auditor_name, c.pubco_name, max(a.fiscal_year), a.month
FROM a_fees_view a, a_auditor b, a_pubco c
WHERE a.auditor_id = b.auditor_id AND a.pubco_id = c.pubco_id
GROUP BY a.auditor_id, a.pubco_id, a.fiscal_year
ORDER BY b.auditor_name, c.pubco_name, a.fiscal_year
Furthermore, I would like to select ALL pubcos from the a_pubco table and not just the one's that are also present in the a_fees_view table. How can I adjust the query above to include all the pubco's that are in both the a_fees_view table and the a_pubco table.

Answer 1

The first part of this problem is a Top-N (or Groupwise-max) query. The usual syntax is as follows:
SELECT x.*
FROM my_table x
JOIN (SELECT grouping_id, MAX(other_field) max_other_field FROM my_table GROUP BY grouping_id) y
ON y.grouping_id = x.grouping_id
AND y.max_other_field = x.other_field;
Consider the following example (inspired by a question asked elsewhere):
I have a table of results from showjumping events. I want to find out in which event each horse did best (and what result they achieved).
SELECT * FROM events;
+----------+----------+-------+
| Event_id | Horse_id | Place |
+----------+----------+-------+
| 601 | 101 | 1 |
| 601 | 102 | 2 |
| 601 | 201 | 3 |
| 601 | 301 | 4 |
| 602 | 201 | 2 |
| 603 | 201 | 3 |
| 701 | 101 | 1 |
| 801 | 301 | 2 |
| 901 | 102 | 7 |
+----------+----------+-------+
From inspection, I can see that horse 101's best result was '1st' which she achieved in two events, so I want both of those rows to be returned.
Horse 102's best result was '2nd', as was horse 201's and horse 301's. But how to construct a query that tells us that? Here's how:
SELECT x.*
FROM events x
JOIN (SELECT horse_id,MIN(place) min_place FROM events GROUP BY horse_id) y
ON y.horse_id = x.horse_id AND y.min_place = x.place;
+----------+----------+-------+
| Event_id | Horse_id | Place |
+----------+----------+-------+
| 601 | 101 | 1 |
| 601 | 102 | 2 |
| 602 | 201 | 2 |
| 701 | 101 | 1 |
| 801 | 301 | 2 |
+----------+----------+-------+