SQL - 组合 DISTINCT 和 INNER JOIN 以及 COUNT(CASE WHEN)

Question

我有 SQL 返回正确的结果。

select accounts.name, count( case when ((( estimated_start_date<='2013-01-01' 
and project.status='closed')

or ( estimated_start_date<='2013-01-01' and project.status='open' 
and estimated_end_date>='2013-04-01')))
then 1 else null end) as Number

from project

inner join project_cstm on project.id=project_cstm.id_c
inner join accounts on project_cstm.account_id_c=accounts.id

group by accounts.name

我返回了良好的结果:

举例:

Telenor 5
Telecom 3

现在我想在 WHERE 子句中添加新字段 BOOKED_DATE 来限制项目数量，仅在该时间间隔内创建一些项目任务。因此，我使用表 inner join project_task 进行 INNER JOIN，结果应该更小，但结果却是这些巨大的数字。不知道如何组合它。

感谢帮助

Telenor 150
Telecom 980

select accounts.name, count( case when ((( estimated_start_date<='2013-01-01' 
and project.status='closed')

or ( estimated_start_date<='2013-01-01' and project.status='open' 
and estimated_end_date>='2013-04-01')))
then 1 else null end) as Number

from project

inner join project_cstm on project.id=project_cstm.id_c
inner join accounts on project_cstm.account_id_c=accounts.id
inner join project_task on project_task.project_id=project.id
where booked_date>'2013-01-01' and booked_date<'2015-01-01'
group by accounts.name

由于表 PROJECT_TASK 中的行，我得到的结果远非正确的巨大结果。怎么限制呢？我尝试输入 ... count(distinct case when ... 但结果始终为 1。

所以我必须以某种方式限制这个值，但我不是这样

Answer 1

您为项目的每项任务数 1，这就是您有这么多的原因。 对于每个项目，您只需将计数增加 1 次。

您想要计算不同的项目，因此不要仅计算 1，而是计算不同的项目 ID:

select accounts.name
     , count( distinct  -- here distinct
        case when ((( estimated_start_date<='2013-01-01' and project.status='closed')
                 or ( estimated_start_date<='2013-01-01' and project.status='open' and estimated_end_date>='2013-04-01')))
        then project.id -- here project id
        else null 
        end) as Number
from project
    inner join project_cstm 
        on project.id=project_cstm.id_c
    inner join accounts 
        on project_cstm.account_id_c=accounts.id
    inner join project_task 
        on project_task.project_id=project.id
where booked_date>'2013-01-01' 
and booked_date<'2015-01-01'
group by accounts.name