Oracle 'Invalid Identifier' in sub-query - sql

Question

I'm having an issue with converting a view from PostgreSQL to Oracle when a sub-query is referencing a column in the outer query.
This issue seems to have been discussed here several times but I have been unable to get any of the fixes to work with my specific query.
The query's purpose is to get a mobile devices last recorded position and get the distance in KM from it's closest checkpoint/Geo-boundary and it references 3 separate tables: devices, device_locations and checkpoints.
SELECT
d.id,
dl.latitude AS last_latitude,
dl.longitude AS last_longitude,
(SELECT * /* Get closest 'checkpoint' to the last device position by calculating the Great-circle distance */
FROM (
SELECT
6371 * acos(cos(dl.latitude / (180/acos(-1))) * cos(checkpoints.latitude / (180/acos(-1))) * cos((checkpoints.longitude / (180/acos(-1))) - (dl.longitude / (180/acos(-1)))) + sin(dl.latitude / (180/acos(-1))) * sin(checkpoints.latitude / (180/acos(-1)))) AS distance
FROM checkpoints
ORDER BY distance)
WHERE ROWNUM = 1) AS distance_to_checkpoint
FROM devices d
LEFT JOIN ( /* Get the last position of the device */
SELECT l.id,
l.time,
l.latitude,
l.longitude,
l.accuracy
FROM device_locations l
WHERE l.ROWID IN (SELECT MAX(ROWID) FROM device_locations GROUP BY id)
ORDER BY l.id, l.time DESC) dl
ON dl.id = d.id;
I've been stuck on this for a while and hoping someone can put me on the right path, thanks.

Answer 1

This is a follow-up to my other answer. In order to get the checkpoints record with the minimum distance, you'd join with the table and use window functions again to pick the best record. E.g.:
select
device_id,
last_latitude,
last_longitude,
checkpoint_latitude,
checkpoint_longitude,
distance
from
(
select
device_id,
last_latitude,
last_longitude,
checkpoint_latitude,
checkpoint_longitude,
distance,
min(distance) over (partition by device_id) as min_distance
from
(
select
d.id as device_id,
dl.latitude as last_latitude,
dl.longitude as last_longitude,
cp.latitude as checkpoint_latitude,
cp.longitude as checkpoint_longitude,
6371 *
acos(cos(dl.latitude / (180/acos(-1))) *
cos(cp.latitude / (180/acos(-1))) *
cos((cp.longitude / (180/acos(-1))) - (dl.longitude / (180/acos(-1))))
+
sin(dl.latitude / (180/acos(-1))) *
sin(cp.latitude / (180/acos(-1)))
) as distance
from devices d
left join
(
select
id as device_id, latitude, longitude, time,
max(time) over (partition by id) as max_time
from device_locations
) dl on dl.device_id = d.id and dl.time = dl.max_time
cross join checkpoints cp
)
)
where (distance = min_distance) or (distance is null and min_distance is null);
Such queries are easier to write with CROSS APPLY and OUTER APPLY, available as of Oracle 12c.

Answer 2

I see two issues:
Extra comma after you final select column: AS distance_to_checkpoint,
Outer select columns reference an inner table device_locations l, instead of the derived table dl - example: l.latitude should be dl.latitude

Answer 3

First of all: The query doesn't get the last device positions. It gets the records with the highest ROWID per ID which may happen to be the latest entry, but is not at all guaranteed to be.
Then you most probably have an issue with scope. Unfortunately, names are only valid one level deep, which is an annoying limitation. dl.latitude etc. are probably not valid in your subquery, because it's actually a subquery within a subquery. Anyway, what you are trying to get is the minimum distance, which you can easily get with MIN.
An ORDER BY in a subquery is superfluous in standard SQL. Oracle makes an exception for their ROWNUM technique, but I wouldn't make use of this. (And as mentioned, it's even clumsy for getting a minimum value.) The ORDER BY in the outer join is superfluous anyway.
This is how I would approach the problem:
select
d.id as device_id,
dl.latitude as last_latitude,
dl.longitude as last_longitude,
(
select min(6371 *
acos(cos(dl.latitude / (180/acos(-1))) *
cos(cp.latitude / (180/acos(-1))) *
cos((cp.longitude / (180/acos(-1))) - (dl.longitude / (180/acos(-1))))
+
sin(dl.latitude / (180/acos(-1))) *
sin(cp.latitude / (180/acos(-1)))
)
)
from checkpoints cp
) as distance
from devices d
left join
(
select
id as device_id, latitude, longitude, time,
max(time) over (partition by id) as max_time
from device_locations
) dl on dl.device_id = d.id and dl.time = dl.max_time;