聚合 SQL 中缺少布爾值的行

Question

我有以下 SQL 腳本，它從PostgreSQL數據庫視圖表中返回以下數據。

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	感應器	ts	速度	溫度	高速	高溫	距離
abcdef	abc1	1616370867010	25	32			52
abcdef	a2bc	1616370867008	27	35		噸	51
abcdef	ab3c	1616370867006	26	30			50
abcdef	abc1	1616370867005	24	36		噸	50
abcdef	a2bc	1616370867004	27	31			50
abcdef	abc1	1616370867002	21	30	噸		48
abcdef	ab3c	1616370867000	22	33	F		46

我想聚合這些行，以便我擁有每個 sensorid 的 ts、速度、溫度、距離的最新讀數。 對於布爾高速和高溫，如果沒有可用的 Boolean 值，我想要最新的可用 Boolean 值或空單元格。

預期 output

macaddr	感應器	ts	速度	溫度	高速	高溫	距離
abcdef	abc1	1616370867010	25	32	噸	噸	52
abcdef	a2bc	1616370867008	27	35		噸	51
abcdef	ab3c	1616370867006	26	30	F		50

我怎樣才能簡化這個任務？

謝謝。

Answer 1

嗯。 . . 對於除 boolean 列之外的所有列DISTINCT ON都可以。 但是這些布爾值很棘手。 您可以在布爾值上使用一些技巧。

相反，讓我們對ROW_NUMBER()使用 go 來獲取最新的行。 並擺弄 arrays 以獲得最新的 boolean 值：

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;

Answer 2

您可以使用DISTINCT ON （僅在 PostgreSQL afaik 中可用）來簡化此查詢。 你可以做：

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