Aggregating rows in SQL with missing Booleans - sql

Question

I have the below SQL script which returns the following data from a PostgreSQL DB view table.
SELECT
"V_data".macaddr,
"V_data".sensorid,
"V_data".ts,
"V_data".velocity,
"V_data".temp,
"V_data".highspeed,
"V_data".hightemp,
"V_data".distance,
FROM
sensordb."V_data"
WHERE
"V_data".macaddr like '%abcdef'
AND
(
("V_data".sensorid = 'abc1') or ("V_data".sensorid = 'a2bc') or ("V_data".sensorid = 'ab3c')
)
AND
"V_data".ts >= 1616370867000
ORDER BY
"V_data".ts DESC;
Output
macaddr
sensorid
ts
velocity
temp
highspeed
hightemp
distance
abcdef
abc1
1616370867010
25
32
52
abcdef
a2bc
1616370867008
27
35
T
51
abcdef
ab3c
1616370867006
26
30
50
abcdef
abc1
1616370867005
24
36
T
50
abcdef
a2bc
1616370867004
27
31
50
abcdef
abc1
1616370867002
21
30
T
48
abcdef
ab3c
1616370867000
22
33
F
46
I want to aggregate the rows such that I have the latest readings per sensorid for ts, velocity, temp, distance.
For the Booleans highspeed and hightemp, I want the latest available Boolean value or an empty cell if no Boolean value was available.
Expected output
macaddr
sensorid
ts
velocity
temp
highspeed
hightemp
distance
abcdef
abc1
1616370867010
25
32
T
T
52
abcdef
a2bc
1616370867008
27
35
T
51
abcdef
ab3c
1616370867006
26
30
F
50
How could I simplify this task?
Thanks.

Answer 1

You can use DISTINCT ON (available only in PostgreSQL afaik) to simplify this query. You can do:
with
q as (
-- your query here
)
select
l.macaddr, l.sensorid, l.ts, l.velocity, l.temp,
s.highspeed, t.hightemp,
l.distance
from (
select distinct on (sensorid) *
from q
order by sensorid, ts desc
) l
left join (
select distinct on (sensorid) *
from q
where highspeed is not null
order by sensorid, ts desc
) s on s.sensorid = l.sensorid
left join (
select distinct on (sensorid) *
from q
where hightemp is not null
order by sensorid, ts desc
) t on t.sensorid = l.sensorid

Answer 2

Hmmm . . . For all but the boolean columns DISTINCT ON would work. But those booleans are tricky. You could use some tricks on booleans.
Instead, let's go for ROW_NUMBER() to get the most recent row. And fiddle with arrays to get the most recent boolean values:
SELECT d.macaddr, d.sensorid,
MAX(d.ts) as ts,
MAX(d.velocity) FILTER (WHERE seqnum = 1) as velocity,
MAX(d.temp) FILTER (WHERE seqnum = 1) as temp,
(ARRAY_REMOVE(ARRAY_AGG(d.highspeed ORDER BY ts DESC), NULL))[1] as highspeed,
(ARRAY_REMOVE(ARRAY_AGG(d.hightemp ORDER BY ts DESC), NULL))[1] as hightemp
MAX(d.distance) FILTER (WHERE seqnum = 1)
FROM (SELECT d.*,
ROW_NUMBER() OVER (PARTITION BY d.macaddr, d.sensorid ORDER BY ts DESC) as seqnum
FROM sensordb."V_data" d
WHERE d.macaddr like '%abcdef' AND
d.sensorid IN ('abc1', 'a2bc', 'ab3c') AND
d.ts >= 1616370867000
) d
GROUP BY d.macaddr, d.sensorid
ORDER BY d.ts DESC;