PostgreSQL CROSS JOIN 查询问题

Question

我想改进以下查询：

WITH calendar as (
      SELECT d
      FROM generate_series(
'2015-01-01'::timestamp, '2020-12-01'::timestamp, interval '1 month'
) d
     )
     
SELECT c.d::date AS ord_date,
       n.id,
       coalesce(nb_cit,0) as nb_cit
FROM (SELECT distinct t.id from "data".taxonomie t where id = '30092') n CROSS JOIN
     calendar c
left join 
(select date_trunc('month', i2.date_d) as mon, count(c2.id) as nb_cit
from "data".inventaire i2, "data".citation c2 where i2.id = c2.id_inv and c2.id_taxo = '30092'
group by mon) s
on c.d = s.mon

它在我设置一个 id 时起作用（在 from 和 left 连接中）。但是我的想法是得到所有 id 的结果。

如果我不设置这个标识符，无论标识符是什么，我都会得到相同的结果。我想我必须从左侧连接中取出“计数（c2.id）”，但我不知道该怎么做。

欢迎帮助！

此致，马蒂亚斯

Answer 1

我认为您只想在子查询中也通过 id 进行聚合：

SELECT c.d::date AS ord_date,
       n.id,
       coalesce(s.nb_cit, 0) as nb_cit
FROM (SELECT DISTINCT t.id FROM "data".taxonomie t) n CROSS JOIN
     calendar c LEFT JOIN
     (SELECT c2.id_taxo, date_trunc('month', i2.date_d) as mon, count(c2.id) as nb_cit
      FROM "data".inventaire i2 JOIN
           "data".citation c2 
           ON i2.id = c2.id_inv 
      GROUP BY c2.id_taxo, mon
     ) s
     ON c.d = s.mon AND n.id = s.id_taxo;

PostgreSQL CROSS JOIN 查询问题

PostgreSQL CROSS JOIN query issue

sql

postgresql

cross-join