PostgreSQL CROSS JOIN 查詢問題

Question

我想改進以下查詢：

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

它在我設置一個 id 時起作用（在 from 和 left 連接中）。 但我們的想法是為所有 id 生成結果。

如果我不設置此標識符，無論標識符是什么，我都會得到相同的結果。 我想我必須從左連接中取出“count（c2.id）”，但我不知道該怎么做。

歡迎幫助！

最好的問候， 馬蒂亞斯

Answer 1

我認為您只想在子查詢中按 id 進行聚合：

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;