PostgreSQL MAX and GROUP BY

The shortest (and possibly fastest) query would be with DISTINCT ON, a PostgreSQL extension of the SQL standard DISTINCT clause:

SELECT DISTINCT ON (1)       id, count, yearFROM   tblORDER  BY 1, 2 DESC, 3;

The numbers refer to ordinal positions in the SELECT list. You can spell out column names for clarity:

SELECT DISTINCT ON (id)       id, count, yearFROM   tblORDER  BY id, count DESC, year;

The result is ordered by id etc. which may or may not be welcome. It's better than "undefined" in any case.

It also breaks ties (when multiple years share the same maximum count) in a well defined way: pick the earliest year. If you don't care, drop year from the ORDER BY. Or pick the latest year with year DESC.

More explanation, links, a benchmark and possibly faster solutions in this closely related answer:

• Select first row in each GROUP BY group?

Aside: In a real life query, you wouldn't use some of the column names. id is a non-descriptive anti-pattern for a column name, count is a reserved word in standard SQL and an aggregate function in Postgres.

select *from (  select id,          year,         thing,         max(thing) over (partition by id) as max_thing  from the_table) twhere thing = max_thing

or:

select t1.id,       t1.year,       t1.thingfrom the_table t1where t1.thing = (select max(t2.thing)                   from the_table t2                  where t2.id = t1.id);

or

select t1.id,       t1.year,       t1.thingfrom the_table t1  join (     select id, max(t2.thing) as max_thing    from the_table t2    group by id  ) t on t.id = t1.id and t.max_thing = t1.thing

or (same as the previous with a different notation)

with max_stuff as (  select id, max(t2.thing) as max_thing  from the_table t2  group by id) select t1.id,        t1.year,       t1.thingfrom the_table t1  join max_stuff t2     on t1.id = t2.id    and t1.thing = t2.max_thing