一個很多查詢，其中許多有一個記錄

Question

我有用戶表，它有很多屬性。用戶表具有一對多關係。我儘量選擇具有一個屬性在屬性表

select *, count(p.account_id) as c 
form accounts as a 
left join properties as p on a.account_id = p.account_id 
group by p.account_id 
having c = 1 

用戶但這並不似乎工作

Answer 1

SELECT *, count(*) as num from 
accounts as a INNER JOIN properties as p 
ON a.account_id = p.account_id 
group by p.account_id 
having num=1 

Answer 2

你也可以把它作爲第二個請求：

select * 
from (
    SELECT *, p.account_id , count(*) as num 
    from accounts as a 
    INNER JOIN properties as p ON a.account_id = p.account_id 
    group by p.account_id 
) query 
where query.num = 1