如何将字段的和聚合为string_Aggregated值Postgres

Question

下面的查询向我展示了一个学生名单和他们的基本信息。

我想把男孩和女孩的总和相加，而不必为他们显示单独的列。所以我创建了两个列，然后取其最后和并显示在最后一行中。

第1部分

with ext as (
select s.studentid as SID,p.surname AS Lastname,
        p.firstname AS Firstname,
        p.sex AS Gender,
        p.birthdate AS BDate,
        ctf.name as Nation,
      SUM(CASE WHEN p.sex = 'MALE' THEN 1 ELSE 0 END) AS BoyCount,
      SUM(CASE WHEN p.sex = 'FEMALE' THEN 1 ELSE 0 END) AS GirlCount
from students s
        join pupil p on p.id = s.pupilid
        join pupilnation pn on pn.pupilid = p.id
        join country ctf on ctf.id = pn.coutnryid
        ...   
group by s.studentid, p.surname, p.firstname,p.sex,p.birthdate,ctf.name
)

Part2

select SID,Lastname,Firstname,Gender,BDate,Nation
from ext
union all
select 'Students: ' || cast(count(SID) as varchar(6)), 
    null as Lastname, 
    null as Firstname,
    'Boys: ' || cast(sum(boycount) as varchar(6)) || '   Girls: ' || cast(sum(girlcount) as varchar(6)),
    null as Bdate,
    string_agg(distinct Nation,',')

结果

SID     Firstname   Gender  Bdate       Nation
723785  Saria       FEMALE  20.01.2012  France
45949   Wenzel      MALE    08.11.2011  Germany
3373    Constantin  MALE    19.03.2006  Germany
727578  Laurin      MALE    08.04.2012  Germany
157     Valerian    MALE    15.01.2008  UK
595959  Attila      MALE    08.06.2012  USA
4172    Sophie      FEMALE  01.11.2004  France
693465  Ibrahim     MALE    16.05.2011  Belgium
…                   
…                   
12 Students         8 Males 4 Females   Germany, France, UK, US, Ughanda

预期结果

我希望将每个国家的最后总和以字符串聚合的形式附加到其字符串中。这是否可能如下文所示？德国: 5，法国: 3，英国: 2，美国: 1，乌甘达:1

SID     Firstname   Gender  Bdate       Nation
723785  Saria       FEMALE  20.01.2012  France
45949   Wenzel      MALE    08.11.2011  Germany
…                   
…                       
12 Students         8 Males 4 Females   Germany: 5, France: 3, UK: 2, US: 1, Ughanda: 1

Answer 1

您可以通过Nation在select中编写子查询select，然后使用string_agg函数。

select SID,Lastname,Firstname,Gender,BDate,Nation
from ext
union all
select 'Students: ' || cast(count(SID) as varchar(6)), 
    null as Lastname, 
    null as Firstname,
    'Boys: ' || cast(sum(boycount) as varchar(6)) || '   Girls: ' || cast(sum(girlcount) as varchar(6)),
    null as Bdate,
    (
        select  string_agg(cnt , ', ') from 
        (
          SELECT Nation||':'||COUNT(*) cnt
          FROM ext
          GROUP BY Nation
        ) t1
    )
FROM ext

或者您可以使用CROSS JOIN来制作它。

SELECT 
    'Students: ' || cast(totalCnt as varchar(6)), 
    null as Lastname, 
    null as Firstname,
    'Boys: ' || cast(boyCnt as varchar(6)) || '   Girls: ' || cast(girlCnt as varchar(6)),
    null as Bdate,
    v.Nation
FROM (
    select  
       sum(boycount) boyCnt,
       sum(girlcount) girlCnt,
       count(SID) totalCnt
    FROM ext
) t1 
CROSS JOIN (
  select string_agg(cnt , ', ') Nation from 
  (
    SELECT Nation||':'||COUNT(*) cnt
    FROM ext
    GROUP BY Nation
  ) t1
) v