mysql - SQL Count() child Rows 基于来自 Parent 的值

Question

我有一个父表

EventKey   Event Name
1001       Event 1
1002       Event 2
1003       Event 3

这是我的子表

EventKey   EventAssignee
1001       Assignee 11
1001       Assignee 12
1002       Assignee 21
1002       Assignee 22

下面是我的SQL查询

select p.EventKey As Event_Key,
       p.Event_Name As EventName,
       (select count(*) 
        from Child c 
        where c.eventkey = p.eventkey) As Assignee_Count
from ParentTable p

这给我一个 SQL 错误意外标记子项。请让我知道哪里出了问题

我期望输出是

Event_Key Event_Name Assignee_Count
1001      Event 1    2    
1002      Event 2    2
1003      Event 3    0

Answer 1

像这样尝试:

select p.EventKey As EventKey , p.EventName As EventName, count(c.assignee) As Assignee_Count
from Parent p left join child c on p.EventKey=c.EventKey 
group by p.EventKey,p.EventName