从左连接表中按计数分组

Question

这是我的疑问：

$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

现在这可行，但它正在计算重复的潜在客户。当我将a.id_lead添加到群组中时，它会弄乱一切。 assignments表中有一列名为id_lead，我希望count（）（delivered）计算按id_lead分组的分配总数，以便忽略超过1行且具有相同的id_lead。

Answer 1

这是什么意思？ ：

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

它与您的查询相同，只是它不计算a中记录的总数，而只计算不同的非空值的数量< / em> in a.id_lead。

（如果不是你的意思，那么请澄清。）