PostgreSQL SELECT JOIN - sql

Question

I have a problem with making a proper SELECT for my exercise:
There are two tables that I have created:
1. Customer
2. Order
ad. 1
CREATE TABLE public."Customer"
(
id integer NOT NULL DEFAULT nextval('"Customer_id_seq"'::regclass),
name text NOT NULL,
surname text NOT NULL,
address text NOT NULL,
email text NOT NULL,
password text NOT NULL,
CONSTRAINT "Customer_pkey" PRIMARY KEY (id),
CONSTRAINT "Customer_email_key" UNIQUE (email)
)
ad.2
CREATE TABLE public."Order"
(
id integer NOT NULL DEFAULT nextval('"Order_id_seq"'::regclass),
customer_id integer NOT NULL,
item_list text,
order_date date,
execution_date date,
done boolean DEFAULT false,
confirm boolean DEFAULT false,
paid boolean DEFAULT false,
CONSTRAINT "Order_pkey" PRIMARY KEY (id),
CONSTRAINT "Order_customer_id_fkey" FOREIGN KEY (customer_id)
REFERENCES public."Customer" (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
)
Please do not mind how columns properties were set.
The problem I have is following:
How to make a SELECT query which will give me as a result ids and emails of customers who have ordered something after '2017-09-15'
I suppose that this should go with JOIN but none of the queries I tried have worked :/.
Thanks!

Answer 1

You should post the queries that you tried, but in the meantime try this. It's a simple join :
SELECT DISTINCT id
, email
FROM public."Customer" c
JOIN public."Order" o
ON c.id = o.customer_id
WHERE order_date > '2017-09-15'

Answer 2

In table "Order" you just need to add current constraint for customer id:
customer_id integer REFERENCES Customer (id)
for more information check this page:
https://www.postgresql.org/docs/9.2/static/ddl-constraints.html
So, the query should be like this:
SELECT id, email
FROM Customer
INNER JOIN Order
ON (Order.customer_id = Customer.id)
WHERE order_date >= '2017-09-15'
Also, the useful docs you can check: https://www.postgresql.org/docs/current/static/tutorial-join.html