剩下兩個表連接一個，而不是從連接中獲取所有數據

Question

我有一張票表，如下所示：

tickets:
id       integer primary key
home_org varchar

有一個homeorgs表，其中包含所有家庭組織，並包括如下的部門代碼：

homeorgs:
home_org      varchar
division_code varchar

我希望能夠顯示每個部門每個月的門票數量，即使某個特定部門沒有提交任何門票。 對於沒有票證的部門，我需要顯示0（零）。

這是SQL：

select 
       count(t.id) as ticket_count,
       to_number(to_char(t.submitdate,'MM'), '99') as mon,
       to_number(to_char(t.submitdate,'YYYY'), '9999') as yr,
       nd.division_key 
  from homeorgs as h 
       LEFT JOIN tickets as t
           ON t.home_org = h.home_org 
           and t.submitdate >= '2018-02-01 00:00:00'
           and t.submitdate <= '2018-02-28 23:59:59'
  where t.home_org is not null
 group by h.division_key, mon, yr
 order by yr, mon, h.division_key 

此sql不會引入沒有提交票證的homeorg行。

我在這里做錯了什么？

Answer 1

只需刪除“ t.home_org不為空”，這可以防止票證表中的記錄不匹配。

  select 
       count(t.id) as ticket_count,
       to_number(to_char(t.submitdate,'MM'), '99') as mon,
       to_number(to_char(t.submitdate,'YYYY'), '9999') as yr,
       nd.division_key 
  from homeorgs as h 
       LEFT JOIN tickets as t
           ON t.home_org = h.home_org 
           and t.submitdate >= '2018-02-01 00:00:00'
           and t.submitdate <= '2018-02-28 23:59:59'
 group by h.division_key, mon, yr
 order by yr, mon, h.division_key

Answer 2

您的問題可能只是where子句。 這是為查詢的其他部分建議更簡單的邏輯：

select count(t.id) as ticket_count,
       extract(month from t.submitdate) as mon,
       extract(year from t.submitdate) as yr,
       h.division_key 
from homeorgs h left join
     tickets as t
    on t.home_org = h.home_org and
       t.submitdate >= '2018-02-01' and
       t.submitdate < '2018-03-01'
group by h.division_key, mon, yr
order by yr, mon, h.division_key ;

就個人而言，我不會將年和月分成不同的列。 我只是將日期截斷到月初：

select count(t.id) as ticket_count, date_trunc('month', t.submitdate) as yyyymm,
       h.division_key 
from homeorgs h left join
     tickets as t
    on t.home_org = h.home_org and
       t.submitdate >= '2018-02-01' and
       t.submitdate < '2018-03-01'
group by h.division_key, yyyymm
order by yyyymm, h.division_key ;