filtering with statement without using from - sql

Question

I want to count products showed in events between two dates. I have to fill 9 columns, each with other product type.
I would like to ask you if there are possibility to short this statement.
Below sql is first working but not effective attempt.
with events(event_id, customer_id) as (
select * from event
where start_date >= :stare_date
and end_date <= :end_date
),
select
(select count(*) from event_product where event_id in (select event_id from events where customer_id = customer.customer_id) and product_type = 'YLW') customer_ylw_products -- it works but its ugly and non effective
-------
-- repeat seven times for other type of products
-------
(select count(*) from event_product where event_id in (select event_id from events where customer_id = customer.customer_id) and product_type = 'RTL') customer_rtl_products
from customer
;
Notice that line
(select event_id from events where customer_id = customer.customer_id)
repeats about 9 times.
I've been trying to short this one by add following:
with events(event_id, customer_id) as (
select * from event
where start_date >= :stare_date
and end_date <= :end_date
),
**customer_events (event_id, customer_id) as (select * from events)**
select
(select count(*) from event_product where event_id in (select event_id from customer_events) and product_type = 'RTL') customer_rtl_products
from customers
where customer_events.customer_id = customer.customer_id -- doesnt works
having customer_events.customer_id = customer.customer_id -- doesnt works

Answer 1

Why don't you use case expressions?
WITH
events (event_id, customer_id)
AS (
SELECT
*
FROM event
WHERE start_date >= :stare_date
AND end_date <= :end_date
)
SELECT
*
FROM customer
LEFT JOIN (
SELECT
event_product.customer_id
, COUNT(CASE
WHEN event_product.product_type = 'YLW' THEN 1 END) AS count_YLW
, COUNT(CASE
WHEN event_product.product_type = 'RTL' THEN 1 END) AS count_RTL
FROM event_product
INNER JOIN events
ON event_product.event_id = events.event_id
GROUP BY
event_product.customer_id
) ev_counts
ON customer.customer_id = ev_counts.customer_id
;
You could do this without the CTE too if you prefer, just use what you currently have in the CTE as a derived table where events is now placed in the inner join.
footnote select * is a convenience only I don't know what fields are to be used, but they should be specified.

Answer 2

#Used_By_Already thanks for inspire me with inner joins between event_product and event and that Event_product doesnt have column customer_id so I simply added it!
That's my solution
with events(event_id, customer_id) as (
select * from event
where start_date >= :stare_date
and end_date <= :end_date
),
product_events (customer_id, product_type) as (
select event.customer_id, event_product.product_type
from events,event_product
where event_product.event_id = event.event_id and event_product.product_type in (''product_types'')
)
select
(select count(*) from product_events where customer_id = customer.customer_id and product_type = 'RTL') customer_rtl_products
from customers;
Performance for 50 rows in search increased from 45 seconds to only 5!
Thank you so much!