Getting a distinct value from one column if all rows matches a certain criteria

I’m trying to find a performant and easy-to-read query to get a distinct value from one column, if all rows in the table matches a certain criteria.

I have a table that tracks e-commerce orders and whether they’re delivered on time, contents and schema as following:

> select * from orders;
+----+--------------------+-------------+
| id | delivered_on_time  | customer_id |
+----+--------------------+-------------+
|  1 |                  1 |           9 |
|  2 |                  0 |           9 |
|  3 |                  1 |          10 |
|  4 |                  1 |          10 |
|  5 |                  0 |          11 |
+----+--------------------+-------------+

I would like to get all distinct customer_id’s which have had all their orders delivered on time. I.e. I would like an output like this:

+-------------+
| customer_id |
+-------------+
|          10 |
+-------------+

What’s the best way to do this?

I’ve found a solution, but it’s a bit hard to read and I doubt it’s the most efficient way to do it (using double CTE’s):

> with hits_all as (
    select memberid,count(*) as count from orders group by memberid
),
hits_true as
    (select memberid,count(*) as count from orders where hit = true group by memberid)
select
    *
from
    hits_true
inner join
    hits_all on
        hits_all.memberid = hits_true.memberid
        and hits_all.count = hits_true.count;
+----------+-------+----------+-------+
| memberid | count | memberid | count |
+----------+-------+----------+-------+
|       10 |     2 |       10 |     2 |
+----------+-------+----------+-------+

Answer

You use group by and having as follows:

select customer_id
from orders
group by customer_id
having sum(delivered_on_time) = count(*)

This works because an ontime delivery is identified by delivered_on_time = 1. So you can just ensure that the sum of delivered_on_time is equal to the number of records for the customer.