Postgres - 仅为一对多关系获取一行

Question

我在 Postgres 中有两个 Table。它们之间是一对多的关系。

经理Table

Id    Designation  
1     Manager

团队成员Table

Id    Designation  Report_To (ManagerId) 
4     INFRA ENG    1
2     SOFT ENG     1
3     TEAM LEAD    1

我必须以这样一种方式获取记录，即我只获得一个经理的一行，并将 TeamMember 指定为单独的列，如下所示：

结果：

ManagerId    INFRA  SOFT  TEAM
1            4      2     3

我尝试使用 LEFT JOIN，但它给了我 3 行。

他将不胜感激任何帮助。

Answer 1

您可以进行条件聚合：

select report_to as manager_id, 
    max(id) filter(where designation = 'INFRA ENG') as infra,
    max(id) filter(where designation = 'SOFT ENG')  as soft,
    max(id) filter(where designation = 'TEAM LEAD') as team
from teammember 
group by report to

请注意，您无需携带 manager table 即可获得您显示的结果。但是如果你出于其他原因想要它，你可以 join:

select m.*, 
    max(tm.id) filter(where tm.designation = 'INFRA ENG') as infra,
    max(tm.id) filter(where tm.designation = 'SOFT ENG')  as soft,
    max(tm.id) filter(where tm.designation = 'TEAM LEAD') as team
from manager m
inner join teammember tm on tm.report_to ) m.id
group by m.id

Postgres - 仅为一对多关系获取一行

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