Clojure: remove from list

Source: How can I remove specific element from a list?
Tip: use a set.

;; Remove elements:
(remove #{3 5} [1 2 3 4 5 6 7 8 9])

;; Keep elements:
(keep #{7 5 3} [1 2 3 4 5 6 7 8 9])

;; Check if element exists:
(some #{5} [1 2 3 4 5 6 7 8 9])

Redshift epoch

Source: Redshift Epochs and Timestamps

select rating_date, extract('epoch' from rating_date::timestamp) as rating_date_epoch
from eu_db1.ft_rated_cdr
where extract('epoch' from cdr_date::timestamp) = 1561504138
and charged_co_id = 296661

PostgreSQL: distinct but only for one column

Source: Postgres: Distinct but only for one column
Problem: The following returns 2 distinct network_id for the same mccmnc_code.

with toto as (
    select mccmnc_code from (values (24024)) as x(mccmnc_code)
)
select dt_mccmnc.mccmnc_code, dt_mccmnc.network_id, dt_mccmnc.country_id
from toto
left join shared_db.dt_mccmnc 
    on dt_mccmnc.mccmnc_code = toto.mccmnc_code
    and dt_mccmnc.master_country_flg is true
    and localtimestamp(0) <@ dt_mccmnc.validity_period

-- mccmnc_code network_id country_id
-- 24024 1828 297
-- 24024 1816 297

So as to keep only one of the rows, use the following:

with toto as (
    select mccmnc_code from (values (24024)) as x(mccmnc_code)
)
select distinct on (dt_mccmnc.mccmnc_code) dt_mccmnc.mccmnc_code, dt_mccmnc.network_id, dt_mccmnc.country_id
from toto
left join shared_db.dt_mccmnc 
    on dt_mccmnc.mccmnc_code = toto.mccmnc_code
    and dt_mccmnc.master_country_flg is true
    and localtimestamp(0) <@ dt_mccmnc.validity_period

-- mccmnc_code network_id country_id
-- 24024 1828 297