On 1/3/19 2:52 μ.μ., Thomas Kellerer wrote:
> Ila B. schrieb am 01.03.2019 um 11:51:
>> Hello,
>>
>> I’m working on a health database and I’m trying to extract the most popular prescription codes from a custom table I
structuredlike this:
>>
>> Year - Code - Count(code)
>>
>> I want to extract the 3 codes with maximum count for each year. I know I should be using rank() but I don’t really
understandhow this works.
>> I am using pgAdmin4 version 3.5 with PostgreSQL 10.6 on Windows 10 Pro and no permission to update.
> Something along the lines:
>
> select code, year, "count"
> from (
> select code, year, "count",
> dense_rank() over (partition by code, year order by "count" desc) as rnk
> from the_table
> ) t
> where rnk <= 3;
Yup, that's the idea
select qryout.* FROM (select qry.*,dense_rank() OVER (ORDER BY count DESC) FROM (select id_1,year_built,count(*) from
vesselsWHERE year_built IS NOT NULL AND year_built<>'' group by id_1,year_built
ORDER BY COUNT(*) DESC) as qry ) qryout WHERE dense_rank<=3;
id_1 | year_built | count | dense_rank
------+------------+-------+------------
94 | 2009 | 11 | 1
97 | 2010 | 10 | 2
94 | 2011 | 10 | 2
94 | 1975 | 9 | 3
94 | 1976 | 9 | 3
(5 rows)
or
select qryout.* FROM (select qry.*,dense_rank() OVER (ORDER BY count DESC) FROM (select distinct
id_1,year_built,count(*)OVER (partition by id_1,year_built) from vessels WHERE year_built IS NOT NULL
AND year_built<>'') as qry ) qryout WHERE dense_rank<=3;
id_1 | year_built | count | dense_rank
------+------------+-------+------------
94 | 2009 | 11 | 1
97 | 2010 | 10 | 2
94 | 2011 | 10 | 2
94 | 1975 | 9 | 3
94 | 1976 | 9 | 3
(5 rows)
>
--
Achilleas Mantzios
IT DEV Lead
IT DEPT
Dynacom Tankers Mgmt