Joining table which may not exist with where clause

I have two tables. Let’s say they are:

table customers: id, name
table orders: id, customer_id, is_finished(boolean), order_sum 

I’d like to make a join to get customer name, number of orders which he/she has finished and sum of money which he/she has spent in total

So I’m making this SQL query:

SELECT c.name,
       coalesce(count(o.id), 0)      AS orders_count,
       coalesce(sum(o.order_sum ), 0) AS total_spent
FROM customers c
         LEFT OUTER JOIN orders o on c.id = o.user_id
WHERE c.id = customer_id
  AND o.is_finished = true
GROUP BY c.name;

If a customer has any finished orders then it will get everything right.

|'John'|3|150|

But if there are no orders or there are orders which are not finished it will not output anything. But my desired output is the following:

|'John'|0|0|

So what is the right way to make such a query so that I’m able to get a result even if a customer has no orders?

I’m using postgreSQL btw

Answer

Just move the condition on the LEFT JOINed table from the WHERE clause to the ON clause of the LEFT JOIN – otherwise it becomes mandatory, and filters out customers that have no matching orders:

SELECT c.name,
    count(o.id)                    AS orders_count,
    coalesce(sum(o.order_sum ), 0) AS total_spent
FROM customers c
LEFT OUTER JOIN orders o ON c.id = o.user_id AND o.is_finished = true
WHERE c.id = customer_id
GROUP BY c.id, c.name;