How to date trunc in HANA - date

Question

I have a query to get the count of buses which travel less than 100 km per day. So I use the query in PostgreSQL
select day,count(*)as bus_count from(
SELECT date_trunc('hour',start_time)::timestamp::date as day,bus_id,sum(distance_two_points) as distance
FROM public.datatable where start_time >= '2015-09-05 00:00:00' and start_time <= '2015-09-05 23:59:59'
group by day,bus_id
) as A where distance<=250000 group by day
The query returns the result
day bus_id distance
___ ________ _________
"2015-09-05 00:00:00" 1 523247
"2015-09-05 00:00:00" 2 135114
"2015-09-05 00:00:00" 3 178560
"2015-09-05 00:00:00" 4 400071
"2015-09-05 00:00:00" 5 312832
"2015-09-05 00:00:00" 6 237075
So I now want to use this same query (achieving same results) in SAP HANA but there is no date trunc function and I also tried
SELECT EXTRACT (DAY FROM TO_DATE (START_TIME, 'YYYY-MM-DD')) "extract" as day,
bus_id, sum(distance_two_points) as distance
FROM public.datatable
where start_time >= '2015-09-05 00:00:00' and start_time <= '2015-09-05 23:59:59'
group by day,bus_id
) as A where distance<=250000 group by day
Any help is appreciated.

Answer 1

SELECT SERIES_ROUND('2013-05-24', 'INTERVAL 1 YEAR', ROUND_DOWN) "result" FROM DUMMY;
SELECT SERIES_ROUND('04:25:01', 'INTERVAL 10 MINUTE') "result" FROM DUMMY;
The SERIES_ROUND from SAP Hana provides similar functionalities as DATE_TRUNC in other vendors.
https://help.sap.com/docs/SAP_HANA_PLATFORM/4fe29514fd584807ac9f2a04f6754767/435ec476ab494ad6b8409f22abec13fe.html?version=2.0.00

Answer 2

Converting to a non-datetime data type is usually not a good idea (additional parsing, encoding, semantics...).
Instead use a less granular datetime data type: daydate in this case.
create column table datatab (start_time seconddate, bus_id int, distance_two_points decimal (10, 2));
insert into datatab values (to_seconddate('05.09.2015 13:12:00'), 1, 50.2);
insert into datatab values (to_seconddate('05.09.2015 13:22:00'), 1, 1.2);
insert into datatab values (to_seconddate('05.09.2015 15:32:00'), 1, 24);
insert into datatab values (to_seconddate('05.09.2015 13:12:00'), 1, 50.2);
insert into datatab values (to_seconddate('05.09.2015 14:22:00'), 2, 1.2);
insert into datatab values (to_seconddate('05.09.2015 16:32:00'), 2, 24);
select to_seconddate(day) as day,count(*) as bus_count from(
SELECT to_date(start_time) as day, bus_id, sum(distance_two_points) as distance
FROM datatab
where start_time between '2015-09-05 00:00:00' and '2015-09-05 23:59:59'
group by to_date(start_time),bus_id
) as A
where distance<=250000
group by day;
The inner query gives you:
DAY BUS_ID DISTANCE
2015-09-05 1 75.40
2015-09-05 2 25.20
So, your seconddate "start_time" is now aggregated as daydate and then converted back to 'seconddate'.

Answer 3

What I prefer is using the seconds_between() or nano100_between() function.
select now(),
add_seconds( to_date('1970.01.01', 'YYYY.MM.DD'),
round(
SECONDS_BETWEEN(
to_date('1970.01.01', 'YYYY.MM.DD'),
now()
)/3600
)*3600
)
from dummy;
This looks a bit ugly but given the to_date() is calculated just once and not for each row and the seconds arithmetic is close to how Hana stores the value internally, it should be the most efficient of the lot.
Also it is the most flexible, round by second, minute, hour, day,... everything below year is fine.
PS: round() supports all round and truncate options.

Answer 4

Assuming your start_time is of some data/time type (e.g. SECONDDATE) you could use
...TO_NVARCHAR(START_TIME, 'YYYY-MM-DD') AS DAY...
Instead of date_trunc... in PostgreSQL

Answer 5

Why don't you use CAST() conversion function?
select
cast( now() as date ) myDate
from dummy;