一个很多查询，其中许多有一个记录

Question

我有用户表，它有很多属性。用户表具有一对多关系。我尽量选择具有一个属性在属性表

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 

用户但这并不似乎工作

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

你也可以把它作为第二个请求：

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