Postgres 11

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SELECT * 
FROM   crosstab(
   $$
   SELECT *
   FROM  (
      VALUES
      (bigint '1546300800', 187923, float8 '1.5')
    , (1546387200,187923,1.5)
    , (1546473600,187923,1.5)
    , (1546560000,187923,1.75)
    , (1546646400,187923,1.75)
    , (1546732800,187923,1.75)
    , (1546819200,187923,1.75)
    , (1546905600,187923,1.5)
    , (1546992000,187923,1.5)
    , (1547078400,187923,1.5)
    , (1547164800,187923,1.5)
    , (1547337600,187924,200)
    , (1547424000,187924,200)
    , (1547510400,187924,200)
    , (1547596800,187924,200)
    , (1547683200,187924,200)
    , (1547769600,187924,200)
    , (1547856000,187924,200)
    , (1547942400,187924,200)
    , (1548028800,187924,200)
    , (1548115200,187924,200)
    , (1548201600,187924,200)
    , (1548288000,187924,200)
    , (1546300800,187926,120)
    , (1546387200,187926,120)
    , (1546473600,187926,120)
    , (1546560000,187926,110)
    , (1546646400,187926,110)
    , (1546732800,187926,110)
    , (1546819200,187926,110)
    , (1546905600,187926,115)
    , (1546992000,187926,115)
    , (1547078400,187926,115)
    , (1547942400,187927,100)
    , (1548028800,187927,100)
    , (1548115200,187927,100)
    , (1548201600,187927,100)
    , (1548288000,187927,100)
   ) t (unixdatetime, gaugesummaryid, value)
   ORDER BY 1,2
   $$
 , 'VALUES (187923), (187924), (187926), (187927)'    -- !!
   ) final_result (unixdatetime int
                 , trace1 float8
                 , trace2 float8
                 , trace3 float8
                 , trace4 float8)

unixdatetime	trace1	trace2	trace3	trace4
1546300800	1.5	null	120	null
1546387200	1.5	null	120	null
1546473600	1.5	null	120	null
1546560000	1.75	null	110	null
1546646400	1.75	null	110	null
1546732800	1.75	null	110	null
1546819200	1.75	null	110	null
1546905600	1.5	null	115	null
1546992000	1.5	null	115	null
1547078400	1.5	null	115	null
1547164800	1.5	null	null	null
1547337600	null	200	null	null
1547424000	null	200	null	null
1547510400	null	200	null	null
1547596800	null	200	null	null
1547683200	null	200	null	null
1547769600	null	200	null	null
1547856000	null	200	null	null
1547942400	null	200	null	100
1548028800	null	200	null	100
1548115200	null	200	null	100
1548201600	null	200	null	100
1548288000	null	200	null	100

SELECT 23