从左联接表按计数分组

Question

这是我的查询：

$select d.*, 
count(a.id) as delivered
from `dealerships` as d
left join `assignments` as a on (a.id_dealership = d.id)
group by d.id
order by d.name asc

现在，此方法有效，但它正在计算重复的潜在客户。 当我将a.id_lead添加到分组依据时，它a.id_lead一切混乱。 assignments表中有一列名为id_lead ，我希望count（）（已delivered ）对由id_lead分组的分配总数进行计数，以便它忽略具有相同id_lead多于一行。

Answer 1

你是这个意思吗？ ：

select d.*, 
count(distinct a.id_lead) as delivered
from `dealerships` as d
left join `assignments` as a on (a.id_dealership = d.id)
group by d.id
order by d.name asc

它与查询相同，除了不计算a 的记录总数 ，它只计算a.id_lead中不同的非空值的a.id_lead 。

（如果这不是您的意思，请进行说明。）