左外部连接在导轨中

Question

I have two objects - Customers & Customer Checkins. Each customer has many checkins and each checkin belongs to one customer.

I need to come up with a query that outputs the complete list of customers together with their checkin count per month. My current query is shown below:

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')")

This query does not list all the customers. What is wrong with my code?

Answer 1

It does not list all the customers because you're only searching for ones with account_id: 139.

Replace

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

With

 customer = Customer...