如何從一個主表中獲取一條記錄，以及如何以一對多的關系從另一張表中獲取有關該表的詳細信息？

Question

作業（主表）

id | name | status

任務（詳細信息表）

id | result | job_id

PS：“結果”列可以將已delivered ， undelivered或unknown作為值

我想通過ID獲得一份工作，並在一行中按結果類型匯總有關它的詳細信息，如下所示：

job_id | job_name | job_status | delivered | undelivered

我嘗試了以下操作，但沒有成功，因為我無法以這種方式使用作業列。 有指針嗎？

select jobs.id, jobs.name, jobs.status, sum(case when tasks.result = 
'deliverable' then 1 end) as deliverable,
sum(case when tasks.result = 'undeliverable' then 1 end) as 
undeliverable from jobs, tasks where jobs.id = 
tasks.job_id and jobs.id = 'We3dJzS4C1wysafM';

Answer 1

我認為您的查詢有兩個問題：

• 不當使用表的別名（ jobs - > veb ）
• 沒有group by

下面還修復了古老的join語法：

select v.id, v.name, v.status,
       sum( (t.result = 'deliverable')::int ) as deliverable,
       sum( (t.result = 'undeliverable')::int ) as undeliverable
from jobs v join
     tasks t
     on v.id = t.job_id and jobs.id = 'We3dJzS4C1wysafM'
group by v.id, v.name, v.status;

Answer 2

使用通用表表達式（CTE）-

with deliverable_tasks as (
select t.job_id, count(*) as deliverable_count
from tasks t
where t.result='deliverable'
group by t.job_id
),
undeliverable_tasks as 
(
select t.job_id, count(*) as undeliverable_count
from tasks t
where t.result='undeliverable'
group by t.job_id
)
select
  j.id,
  j.name,
  j.status,
  dt.deliverable_count,
  ut.undeliverable_count
from jobs j
left join deliverable_tasks dt on dt.job_id=j.id
left join undeliverable_tasks ut on ut.job_id=j.id