Question

I have a table with id, year and count.

I want to get the MAX(count) for each id and keep the year when it happens, so I make this query:

SELECT id, year, MAX(count)
FROM table
GROUP BY id;

Unfortunately, it gives me an error:

ERROR: column “table.year” must appear in the GROUP BY clause or be
used in an aggregate function

So I try:

SELECT id, year, MAX(count)
FROM table
GROUP BY id, year;

But then, it doesn’t do MAX(count), it just shows the table as it is. I suppose because when grouping by year and id, it gets the max for the id of that specific year.

So, how can I write that query? I want to get the id´s MAX(count) and the year when that happens.

Answer 1

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

or:

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

or

select t1.id,
       t1.year,
       t1.thing
from 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.thing
from the_table t1
  join max_stuff t2 
    on t1.id = t2.id 
   and t1.thing = t2.max_thing