Thread: Top 3 values for each group in PGSQL
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. Thank you in advance, Ilaria
On Fri, Mar 01, 2019 at 11:51:24AM +0100, Ila B. wrote: > 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. Consider reading https://www.depesz.com/2012/10/05/getting-top-n-rows-per-group/ Best regards, depesz
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;
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