Postgres distinct union only for specific columns - postgresql

Question

I have two sets of data, one of which is dynamically generated.
If I leave off the column state it works perfectly as that column doesn't really exist, my question is how can I ignore a column for the UNION so that it combines the two datasets (as it is it's the same as UNION ALL). eg I prefer the first table and want any rows from the second dataset ignored if they exist in the first one.
SELECT event_id, start_at, state
FROM event_logs
WHERE start_at BETWEEN current_date AND current_date + interval '3 weeks'
UNION
SELECT id event_id,
GENERATE_SERIES(date_trunc('week', current_date)::date + (extract(isodow from start_at)::int - 1) + start_at::time, current_date + interval '3 weeks', '1 week'::INTERVAL) AS start_at,
'draft' AS state
FROM events
Update, also tried:
WITH future_logs AS (
SELECT id event_id,
GENERATE_SERIES(date_trunc('week', current_date)::date + (extract(isodow from start_at)::int - 1) + start_at::time, current_date + interval '3 weeks', '1 week'::INTERVAL) AS start_at,
'draft' AS state
FROM events)
SELECT future_logs.event_id, future_logs.start_at, future_logs.state
FROM future_logs
LEFT JOIN event_logs ON future_logs.event_id = event_logs.event_id AND future_logs.start_at = event_logs.start_at
WHERE event_logs.start_at BETWEEN current_date AND current_date + interval '3 weeks'
But got too few results 77 vs ~1000 expected.

Answer 1

Just add NOT EXISTS() to the second leg, and you can use UNION ALL to avoid sort/merging.
SELECT event_id, start_at, state
FROM event_logs
WHERE start_at BETWEEN current_date AND current_date + interval '3 weeks'
UNION ALL
SELECT id AS event_id
, generate_series(date_trunc('week', current_date)::date + (extract(isodow from start_at)::int - 1) + start_at::time
, current_date + interval '3 weeks'
, '1 week'::INTERVAL) AS start_at
, 'draft' AS state
FROM events ev
WHERE NOT EXISTS ( SELECT*
FROM event_logs nx
WHERE nx.event_id =ev.id
AND nx.start_at BETWEEN current_date AND current_date + interval '3 weeks' )
;

Answer 2

select DISTINCT ON (date_day) date_day, state from(
SELECT day::date as date_day, null as state
FROM generate_series(now()- interval '2 week'
, now()
, interval '1 day') day
UNION ALL
select distinct
date_trunc('day',e.updated_at) as date_day,
max(des.state) over (partition by date_trunc('day',des.updated_at)) as state
from device_event as des where e.id=49 and e.updated_at >= now() - interval '2 week'
) dba order by 1

Answer 3

I would add one other column taborder into your UNION query to ensure simple ordering of the rows and use window function row_number() over(...) in following way:
SELECT
event_id,
start_at,
state
FROM (
SELECT
event_id,
start_at,
state,
row_number(*) OVER (PARTITION BY event_id, start_at ORDER BY taborder) AS rownum
FROM (
SELECT
event_id,
start_at,
state,
1 AS taborder
FROM original_table
UNION
SELECT
event_id,
start_at,
state,
2 AS taborder
FROM draft_table
) src0
) src1
WHERE rownum = 1
ORDER BY 1, 2, 3