Get data for every second in interval - postgresql

Question

I want to write a query which will results value between timestamp at every second and if value for particular time stamp is not there then it should result zero.for example
Start date time - 27/7/2015 10:00:00
End date time - 27/7/2015 10:05:00
Then result should be
27/7/2015 10:00:00 10 [start date time]
27/7/2015 10:00:01 19
27/7/2015 10:00:02 23
27/7/2015 10:00:03 0 [Value not present in table for this timestamp]
27/7/2015 10:00:04 45
27/7/2015 10:00:05 0 [Value not present in table for this timestamp]
...
27/7/2015 10:05:00 42 [end date time ]
I am trying this query but not getting desired result
SELECT CAST(date_trunc('second', CAST(to_timestamp(t1.timestamp_col,'DD-MM-YYYY HH24:MI:SS')as timestamp without time zone) + interval '1 second') as text)
, NULLIF(t1.y_temperature_col,'00')
FROM historical_trend_data t1
WHERE CAST(to_timestamp(t1.timestamp_col,'DD-MM-YYYY HH24:MI:SS') as timestamp without time zone) BETWEEN CAST(to_timestamp('28/7/2015 10:00:00','DD-MM-YYYY HH24:MI:SS')as timestamp without time zone) AND CAST(to_timestamp('28/7/2015 18:00:00','DD-MM-YYYY HH24:MI:SS') as timestamp without time zone);
This is the Function
CREATE OR REPLACE FUNCTION timestampwise_sp2(IN startdatetime text, IN enddatetime text,
OUT x_time_col text, OUT temperature text)
RETURNS SETOF record AS $BODY$
BEGIN
return query
with simul_data as(
SELECT generate_series(startdatetime::timestamp,
enddatetime::timestamp, '1 Seconds') As x_time_col
)
Select simul_data.x_time_col::text, coalesce(t1.y_temperature_col, '0') AS temperature
from historical_trend_data t1
LEFT JOIN simul_data ON CAST(to_timestamp(t1.timestamp_col,'DD-MM-YYYY HH24:MI:SS') as timestamp without time zone) = simul_data.x_time_col;
END; $BODY$ LANGUAGE plpgsql VOLATILE;
but it is not resulting the desired result

Answer 1

SELECT s.sec AS obs_time, coalesce(t1.y_temperature_col, 0) AS temperature
FROM generate_series('28-07-2015 10:00:00'::timestamp,
'28-07-2015 18:00:00'::timestamp, '1 minute') AS s(sec)
LEFT JOIN t1 ON timestamp_col = s.sec;
The generate_series() function returns a set of records in a sequence, in this case second intervals from a starting point to an ending point. That is left-joined to your actual data and any NULL values for the temperature are converted to 0 with the coalesce() function.
In function form it would be like this:
CREATE FUNCTION timestampwise_sp2(startdatetime timestamp, enddatetime timestamp) AS $$
SELECT to_char(simul_data.x_time_col, 'DD/MM/YYYY HH24:MI:SS') AS x_time_col,
coalesce(t1.y_temperature_col, '0') AS temperature
FROM generate_series($1, $2, '1 second') AS simul_data(x_time_col)
LEFT JOIN historical_trend_data t1
ON to_timestamp(t1.timestamp_col,'DD/MM/YYYY HH24:MI:SS') = simul_data.x_time_col;
$$ LANGUAGE sql STRICT;
Note that this is a sql language function, which is faster than plpgsql.