I do not know when to use DATE_TRUNC and DATE_PART() in a query.
I have not really tried much, just some web searches that I do not fully grasp but I just started learning SQL (Postgres).
They both do very different things. One truncates a date to the precision specified (kind of like rounding, in a way) and the other just returns a particular part of a datetime.
From the documentation:
date_part():
The date_part function is modeled on the traditional Ingres equivalent
to the SQL-standard function extract:
date_part('field', source)
Note that here the field parameter needs to be a string value, not a
name. The valid field names for date_part are the same as for extract.
For historical reasons, the date_part function returns values of type
double precision. This can result in a loss of precision in certain
uses. Using extract is recommended instead.
SELECT date_part('day', TIMESTAMP '2001-02-16 20:38:40');
Result: 16
SELECT date_part('hour', INTERVAL '4 hours 3 minutes');
Result: 4
date_trunct():
The function date_trunc is conceptually similar to the trunc function
for numbers.
date_trunc(field, source [, time_zone ]) source is a value expression
of type timestamp, timestamp with time zone, or interval. (Values of
type date and time are cast automatically to timestamp or interval,
respectively.) field selects to which precision to truncate the input
value. The return value is likewise of type timestamp, timestamp with
time zone, or interval, and it has all fields that are less
significant than the selected one set to zero (or one, for day and
month).
...
Examples (assuming the local time zone is America/New_York):
SELECT date_trunc('hour', TIMESTAMP '2001-02-16 20:38:40');
Result: 2001-02-16 20:00:00
SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40');
Result: 2001-01-01 00:00:00
SELECT date_trunc('day', TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40+00');
Result: 2001-02-16 00:00:00-05
SELECT date_trunc('day', TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40+00', 'Australia/Sydney');
Result: 2001-02-16 08:00:00-05
SELECT date_trunc('hour', INTERVAL '3 days 02:47:33');
Result: 3 days 02:00:00
Related
ERROR: timestamp units "timezone" not supported
That's the error I get for all timezone fields.
Here's a minimal query you can run:
select extract(timezone_hour from now()::timestamptz at time zone 'US/Eastern');
What I want is the utc offset in hours. So this should return -4.
The requirement is that I use a dynamic time zone in the query. So I have a table of "facilities" with time zone strings, and I need to get the current time for each one.
So my end query should look something like this:
SELECT
EXTRACT(timezone_hour from now() with time zone timezone) # timezone is the name of the field
FROM facilities;
I thought I had it for a second with this, but this is giving me my current offset, not the offset of the tz I'm passing:
select
extract(timezone_hour from (select now()::timestamp at time zone 'US/Eastern'))
date_part
-----------
-7
I ended up getting this to work with creating two timestamps, one at utc and one at the desired time zone, but I'll leave this open just in case there's a better solution than my current one:
select
extract(hour from (
select (
select now() at time zone 'US/Eastern') - (select now() at time zone 'UTC')));
date_part
-----------
-4
so I have a table called Value. I am trying to derive the Value for the last hour (HR --> Timestamp(4) with TIME ZONE ) so that I can use it in a conditional statement in this Stored Procedure that I'm building. However, when i try the following, Oracle only returns a Date (01-Jan-19) rather than the previous hour (01-Jan-19 01.00.00.00000000 AM UTC). What am I doing wrong?
select hr
, hr - (1/24) as Converted
from value;
If I try the following, I return '31-DEC-16 12.00.00.000000000 AM' as the value for 'Converted' (no matter what the value for HR is):
select hr
, to_timestamp(hr - (1/24)) as converted
from value;
Which ultimately will be used as the definition of a variable in my stored procedure:
select max(value)
into v_Previous_hour
from value
where hr = hr - (1/24);
Am I missing something here? Thanks in advance.
Try this:
select hr
, cast( hr - (1/24) as timestamp) as Converted
from value;
Also, the query below is not going to do what you think it is.
select max(value)
into v_Previous_hour
from value
where hr = hr - (1/24);
Or you could use INTERVAL:
SELECT TO_CHAR(HR) AS HR,
TO_CHAR(CAST(HR - INTERVAL '1' HOUR - INTERVAL '0.233' SECOND AS TIMESTAMP(4) WITH TIME ZONE)) AS HR_MINUS_ONE_HOUR
FROM VAL;
(Here I subtracted an additional 0.233 seconds just to make sure we were dealing with timestamps, per #AlexPoole's comment on #OldProgrammer's answer).
SQLFiddle here
Oracle only returns a Date (01-Jan-19)
A date still has a time, your client just isn't showing it to you. You can use to_char() to display it explicitly:
select to_char(hr - (1/24), 'YYYY-MM-DD HH24:MI:SS') from ...
It is a date because [that's the result of timestamp - number] arithmetic, and the timestamp is implicitly converted to a date before the subtraction. But you are losing both the fractional seconds and the time zone from your original value. Even if you cast back to a plain timestamp that information isn't recovered, and if you cast back to a timestamp with time zone it imolicitly picks up the current session's time zone, so won't necessarily match.
To keep both you can do what you suggested in your answer, or
select hr - interval '1' hour from ...
In your procedure, declare a variable of the same data type, e.g. (as an nonymous block):
declare
l_hr value.hr%type;
begin
select hr - interval '1' hour
into l_hr
from value
where ... ;
...
end;
Don't be tempted to store or manipulate the value as a string, keep it as its origial data type. It will be easieer to work with, safer and more efficient.
Have a look at this table Matrix of Datetime Arithmetic
When you perform {TIMESTAMP WITH TIME ZONE} - {NUMERIC} then you get DATE value, i.e. you loose the time zone information.
Better use INTERVAL, e.g. hr - INTERVAL '1' HOUR or hr - NUMTODSINTERVAL(1, 'HOUR')
Anyway, I don't understand your question. If you ask "How to grab the previous hour of a timestamp(4) with TIMEZONE column?" then my answer would be
SELECT
EXTRACT(HOUR FROM hr - INTERVAL '1' HOUR) AS Solution_1
TO_CHAR(hr - INTERVAL '1' HOUR, 'HH24') AS Solution_2
FROM ...
Note, solution EXTRACT(HOUR FROM hr - INTERVAL '1' HOUR) always returns the hour of UTC time, whereas TO_CHAR(hr - INTERVAL '1' HOUR, 'HH24') returns hour from the stored time zone.
After 2 hours of hairpulling (and ironically after OldProgrammer was nice enough to provide me with an answer), I found a workaround:
select hr
, hr - numtodsinterval(1, 'hour') as converted
from value;
My goal is to offset timestamps in table Date_times to reflect local timezones. I have a Timezone_lookup table that I use for that, which has a column utc_convert and its values are (2, -1, 5, etc.) depending on the timezone.
I used to use NUMTODSINTERVAL in Oracle to be able to convert the utc_convert values to hours so I can add/subtract from the datetimes in the Date_times table.
For Redshift I found INTERVAL, but that's only hardcoding the offset with a specific number.
I also tried:
SELECT CAST(utc as TIME)
FROM(
SELECT *
,to_char(cast(utc_convert as int)||':00:00', 'HH24') as utc
from Timezon_lookup
)
But this doesn't work as some number in the utc_convert column have negative values. Any ideas?
Have you tried multiplying the offset by an interval:
select current_timestamp + utc_convert * interval '1 hour'
In Oracle, you can use the time zone of the user's session (which means you do not need to maintain a table of time zone look-ups or compensate for daylight savings time).
SELECT FROM_TZ( your_timestamp_column, 'UTC' ) AT LOCAL
FROM Date_times
SQLFIDDLE
In RedShift you should be able to use the CONVERT_TIMEZONE( ['source_timezone',] 'target_timezone', 'timestamp') function rather adding a number of intervals. This would allow you to specify the target_timezone as a numeric offset from UTC or as a time zone name (which would automatically compensate for DST).
Suppose I have given two dates, if difference is one month then it should be display as 30 days.Even months also need to convert into days
I have tried with age( date,now()::timestamp without time zone) but it is giving months-dates-years format. ex: 10 mons 24 days 13:57:40.5265.But I need following way.
For example if two months difference is there then I need output as 60 days.
Don't use the age() function for date/time arithmetic. It only returns "symbolic" results (which are good enough for human representation, but almost meaningless for date/time calculations; compared to the standard difference).
The standard difference operator (-) returns day-based results for both date, timestamp and timestamp with time zone (the former returns days as int, the latter two return day-based intervals):
From the day-based intervals you can extract days with the extract() function:
select current_date - '2017-01-01',
extract(day from now()::timestamp - '2017-01-01 00:00:00'),
extract(day from now() - '2017-01-01 00:00:00Z');
http://rextester.com/RBTO71933
Both of those will give that result.
select make_interval(days => ((extract(epoch from '2016-04-10'::date) - extract(epoch from '2016-02-10'::date))/(60*60*24))::integer)::text;
select format('%1$s days', ((extract(epoch from '2016-04-10'::date) - extract(epoch from '2016-02-10'::date))/(60*60*24))::integer);
How to get the date and time only up to minutes, not seconds, from timestamp in PostgreSQL. I need date as well as time.
For example:
2000-12-16 12:21:13-05
From this I need
2000-12-16 12:21 (no seconds and milliseconds only date and time in hours and minutes)
From a timestamp with time zone field, say update_time, how do I get date as well as time like above using PostgreSQL select query.
Please help me.
There are plenty of date-time functions available with postgresql:
See the list here
http://www.postgresql.org/docs/9.1/static/functions-datetime.html
e.g.
SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40');
Result: 16
For formatting you can use these:
http://www.postgresql.org/docs/9.1/static/functions-formatting.html
e.g.
select to_char(current_timestamp, 'YYYY-MM-DD HH24:MI') ...
To get the date from a timestamp (or timestamptz) a simple cast is fastest:
SELECT now()::date
You get the date according to your local time zone either way.
If you want text in a certain format, go with to_char() like #davek provided.
If you want to truncate (round down) the value of a timestamp to a unit of time, use date_trunc():
SELECT date_trunc('minute', now());
This should be enough:
select now()::date, now()::time
, pg_typeof(now()), pg_typeof(now()::date), pg_typeof(now()::time)