左外连接导轨

Question

我有两个对象 - 客户和客户签到。每个客户有很多签到，每个签到属于一个客户。

我需要提出一个查询，输出完整的客户列表以及他们每月的签到次数。我当前的查询如下所示：

customer = Customer.where(account_id: 139).joins('LEFT JOIN
    customer_checkins on customer_checkins.customer_id =
    customers.id').uniq.select("COUNT(*) as count, customers.created_at as
    created_at, customers.name, customers.telephone, customers.mobile,
    customers.email, customers.gender, customers.city,
    customers.birthday,date_format(customer_checkins.created_at, '%b') as
    'month', customers.id").group("customer_checkins.customer_id,
    date_format(customer_checkins.created_at, '%b %Y')")

此查询未列出所有客户。我的代码有什么问题？

Answer 1

它没有列出所有客户，因为您只搜索 account_id: 139 的客户。

替换

customer = Customer.where(account_id: 139)...

与

 customer = Customer...