Ignore the first and last row in a query result - postgresql

Question

I'm trying to do a query where I want to ignore the first and the last row of the result query.
My result query is retrieving the sum of all mediums in the last hour grouped by 5 minutes.
To ignore the first record I'm using offset(1) and to ignore the last i was trying to do a limit in my id field, ordering by timestamp desc.
My query:
ws_controller_hist=>
SELECT to_timestamp(floor((extract('epoch' FROM TIMESTAMP) / 300)) * 300)
AS timestamp_min,
TYPE,
floor(sum(medium[1]))
FROM default_dataset
WHERE TYPE LIKE 'ap_clients.wlan0'
AND TIMESTAMP > CURRENT_TIMESTAMP - interval '85 minutes'
AND organization_id = '9fc02db4-c3df-4890-93ac-8dd575ca5638'
AND id NOT IN
(SELECT id
FROM default_dataset
ORDER BY TIMESTAMP DESC
LIMIT 1)
GROUP BY timestamp_min,
TYPE
ORDER BY timestamp_min ASC
OFFSET 1;
timestamp_min | type | floor
------------------------+------------------+-------
2017-12-19 14:20:00+00 | ap_clients.wlan0 | 38
2017-12-19 14:25:00+00 | ap_clients.wlan0 | 37
2017-12-19 14:30:00+00 | ap_clients.wlan0 | 39
2017-12-19 14:35:00+00 | ap_clients.wlan0 | 42
2017-12-19 14:40:00+00 | ap_clients.wlan0 | 43
2017-12-19 14:45:00+00 | ap_clients.wlan0 | 44
2017-12-19 14:50:00+00 | ap_clients.wlan0 | 45
2017-12-19 14:55:00+00 | ap_clients.wlan0 | 45
2017-12-19 15:00:00+00 | ap_clients.wlan0 | 43
2017-12-19 15:05:00+00 | ap_clients.wlan0 | 43
2017-12-19 15:10:00+00 | ap_clients.wlan0 | 50
2017-12-19 15:15:00+00 | ap_clients.wlan0 | 52
2017-12-19 15:20:00+00 | ap_clients.wlan0 | 50
2017-12-19 15:25:00+00 | ap_clients.wlan0 | 53
2017-12-19 15:30:00+00 | ap_clients.wlan0 | 49
2017-12-19 15:35:00+00 | ap_clients.wlan0 | 39
2017-12-19 15:40:00+00 | ap_clients.wlan0 | 16
This is not ignoring the last record because i have the same records dont using the subquery " and id not in (select id from default_dataset order by timestamp desc limit 1) "

Answer 1

Wrap your query in an outer query and use lag and OFFSET to do the trick.
SELECT lag(timestamp_min) OVER (ORDER BY timestamp_min) AS timestamp_min,
lag(type) OVER (ORDER BY timestamp_min) AS type,
lag(sum_first_medium) OVER (ORDER BY timestamp_min),
FROM (SELECT to_timestamp(
floor(
(extract('epoch' FROM TIMESTAMP) / 300)
) * 300
) AS timestamp_min,
type,
floor(sum(medium[1])) AS sum_first_medium
FROM default_dataset
WHERE type = 'ap_clients.wlan0'
AND timestamp > current_timestamp - INTERVAL '85 minutes'
AND organization_id = '9fc02db4-c3df-4890-93ac-8dd575ca5638'
GROUP BY timestamp_min, type) lagme
OFFSET 2;

Answer 2

This is probably bit long, but will do exactly as you requested
SELECT z.*
FROM
(SELECT y.*, min(row_number) OVER(), max(row_number) OVER()
FROM
(SELECT x.*, row_number() OVER(ORDER BY timestamp_min)
FROM
(SELECT to_timestamp(floor((extract('epoch' FROM TIMESTAMP) / 300)) * 300)
AS timestamp_min,
TYPE,
floor(sum(medium[1]))
FROM default_dataset
WHERE TYPE LIKE 'ap_clients.wlan0'
AND TIMESTAMP > CURRENT_TIMESTAMP - interval '85 minutes'
AND organization_id = '9fc02db4-c3df-4890-93ac-8dd575ca5638'
AND id NOT IN
(SELECT id
FROM default_dataset
ORDER BY TIMESTAMP DESC
LIMIT 1)
GROUP BY timestamp_min,
TYPE
ORDER BY timestamp_min ASC
) AS x
) AS y
) AS z WHERE row_number NOT IN (min, max)