Is there a scalar function in DB2 to convert a long number to TIMESTAMP?
As #Dan1111 points out; no, there's nothing built in.
However, if you've got a 'long' number (I'm assuming BIGINT), I'm guessing you have a count of seconds (or similar) from the Unix Epoch (1970-01-01 00:00:00.000 UTC). If so, it's easy to 'cheat', and you can use this logic to write your own:
SELECT TIMESTAMP('1970-01-01', '00:00:00') + <your_column> SECONDS
FROM <your_table>
This of course presumes that the count is actually from UTC (and that you plan to interpret the results as such), as daylight savings time (and timezones, to a lesser extent) screws things up royally.
A quick example:
SELECT TIMESTAMP('1970-01-01', '00:00:00') + 1348241581 SECONDS
FROM sysibm/sysdummy1
Yields the expected:
2012-09-21-15.33.01.000000
(GMT, obviously)
Related
I'm interested in knowing the different possibilities to operate with datetimes in SQLite and understand its pros and cons. I did not find anywhere a detailed explanation of all the alternatives.
So far I have learned that
SQLite doesn't actually have a native storage class for timestamps /
dates. It stores these values as NUMERIC or TEXT typed values
depending on input format. Date manipulation is done using the builtin
date/time functions, which know how to convert inputs from the other
formats.
(quoted from here)
When any operation between datetimes is needed, I have seen two different approaches:
julianday function
SELECT julianday(OneDatetime) - julianday(AnotherDatetime) FROM MyTable;
Number of days is returned, but this can be fractional.
Therefore, you can also get some other measures of time with some extra operations. For instance, to get minutes:
SELECT CAST ((
julianday(OneDatetime) - julianday(AnotherDatetime)
) * 24 * 60 AS INTEGER)
Apparently julianday could cause some problems:
Bear in mind that julianday returns the (fractional) number of 'days'
- i.e. 24hour periods, since noon UTC on the origin date. That's usually not what you need, unless you happen to live 12 hours west of
Greenwich. E.g. if you live in London, this morning is on the same
julianday as yesterday afternoon.
More information in this post.
strftime function
SELECT strftime("%s", OneDatetime)-strftime("%s", AnotherDatetime) FROM MyTable;
Number of seconds is returned. Similarly, you can also get some other measures of time with some extra operations. For instance, to get minutes:
SELECT (strftime("%s", OneDatetime)-strftime("%s", AnotherDatetime))/60 FROM MyTable;
More information here.
My conclusion so far is: julianday seems easier to use, but can cause some problems. strftime seems more verbose, but also safer. Both of them provide only as results a single unit (either days or hours or minutes or seconds), but not a combination of many.
Question
1) Is there any other possibility to operate with datetimes?
2) What would be the best way to get directly the difference of two datetimes in time format (or date or datetime), where datetime would be formatted as 'YYYY-mm-dd HH:MM:SS', and the result would be something in the same format?
I would have imagined that something like the following would work, but it does not:
SELECT DATETIME('2016-11-04 08:05:00') - DATETIME('2016-11-04 07:00:00') FROM MyTable;
> 01:05:00
Julian day numbers are perfectly safe when computing differences.
The only problem would be if you tried to convert them into a date by truncating any fractional digits; this would result in noon, not midnight. (The same could happen if you tried to store them in integer variables.) But that is not what you're doing here.
SQLite has no built-in function to compute date/time differences; you have to convert date/time values into some number first. Whether you use (Julian) days or seconds does not really matter from a technical point of view; use whatever is easier in your program.
If you started with a different format, you might want to convert the resulting difference back into that format, e.g.:
time(difference_value, 'unixepoch') -- from seconds to hh:mm:ss
time(0.5 + difference_value) -- from Julian days to hh:mm:ss
I have read in this online PostgreSQL documentation... http://www.postgresql.org/docs/9.4/static/datatype-datetime.html#INTERVAL-STYLE-OUTPUT-TABLE
in the point 8.5.5 something about how to tweak the default Interval Output. . I mean the default interval is shown like this...
00:00:00.000 (if the timedifference is lower than a day or month or year)
1 day 00:00:00.000 (if the timedifference reaches days, but is lower than a month or a year)
1 month 1 day 00:00:00.000 (if the timediffence reaches months, but is lower than a year)
1 year 1 month 1 day 00:00:00.000 (if it reaches years, months, days)
it evens uses plurarl cases (years, mons, days) when their values are greater than one.
All these variations make difficult to any other app when SELECTing (query) this interval values (as text) to convert it to a proper time. So I would like postgresql to always show year, month n days, even if their value are 0 (it could be even better if it could show the date part of the interval like this... 01-11-30, adding zeros to the left side when values are less than ten)
I know I can change the interval to text, using to_char() but I really would like to avoid that, I would like some good fellow postgresql programmer to tell me if it is true that there is a way to tweak the Interval Output as is said in the postgresql documentation.
Thanks Advanced.
PD: two more links about the subject
https://my.vertica.com/docs/7.1.x/HTML/Content/Authoring/SQLReferenceManual/Statements/SET/SETDATESTYLE.htm
http://my.vertica.com/docs/6.1.x/HTML/index.htm#13874.htm
You can set the interval output style, but only to one of a few pre-defined formats that are unambigious on input, and that PostgreSQL knows how to parse back into intervals. Per the documentation these are the SQL standard interval format, two variants of PostgreSQL specific syntax, and iso_8601 intervals.
If you want something familiar and easy to parse, consider using:
SET intervalstyle = 'iso_8601'
and using an off-the-shelf parser for ISO1601 intervals.
I am in the process of optimizing some UniVerse data access code we have which uses UniObjects. After some experimentation, it seems that using a UniSession.OConv call to parse certain things such as decimal numbers (most we have a MR4 or MR2 or MR2$) and dates (almost all are D2/) is extremely slow (I think it might make a call back to the server to parse it).
I have already built a parser for the MR*[$] codes, but I was wondering about the dates as they are stored so I can build one for D2/. Usually they seem to be stored as a 5 digit number. I thought it could be number of days since the Unix Epoch since our UniVerse server runs on HP-UX, but after finding '15766' as a last modified date and multiplying it by 86400 (seconds per day), I got March 02, 2013 which doesn't make sense as a last modified date since as far as I know that is still in the future.
Does anyone know what the time base of these date numbers are?
It is stored as a number of days. Just do a conversion on 0 and you will get the start date.
Edit:
As noted by Los, the Epoch used in UniVerse (and UniData) is 31st Dec 1967.
In Universe and any other Pick database, Dates and Times are stored as separate values.
The internal date is the number of days before of after 31/12/1967, which is day zero.
The internal time is the number of seconds after midnight. It can be stored as a decimal but is not normally.
In TCL there is a CDT command (stands for Convert Date) that converts dates from human readable to numeric and and vice versa:
CDT 9/28/2017
* Result: 18169
CDT 18169
* Result: 09/28/2017
How can i convert 2012-04-12 00:00:00 to a unix timestamp in DB2. is there any inbuild function available in sql s
Thank you.
Using the DAYS and MIDNIGHT_SECONDS is much more precise than TIMESTAMPDIFF:
SELECT
86400*(DAYS(CURRENT TIMESTAMP - CURRENT TIMEZONE)-DAYS('1970-01-01'))
+ MIDNIGHT_SECONDS(CURRENT TIMESTAMP - CURRENT TIMEZONE)
"UNIX_TIMESTAMP"
FROM SYSIBM.SYSDUMMY1
By Unix timestamp I assume you mean the number of seconds (or whatever) since 1970-01-01 00:00:00 UTC.
There is no built in functionality for this in DB2 (as of V6R1).
You're also up against the following issues:
All timestamps in DB2 are 'local time' - they contain no timezone information, and all CURRENT_TIMESTAMP writes are based on what time the requesting system thinks it is, not the host.
Daylight savings time changes frequently. You would need to add overhead to manage this for your conversion.
The TIMESTAMPDIFF function returns an estimate, not an exact value. You could probably survive for the years/months durations, over sufficient differences, but days aren't likely to cut it.
Timestamp arithmetic is imprecise (among other things, months are assumed to be always 30 days in length...)
Your best bet will be to start using DAYS (which returns the number of days since 0001-01-01). Keep in mind you better do everything in UTC, because it will not take DST into account.
I am converting an Unix script with a SQL transact command to a PostgreSQL command.
I have a table with records that have a field last_update_time(xtime) and I want to select every record in the table that has been updated within a selected period.
Say, the current time it 05/01/2012 10:00:00 and the selected time is 04/01/2012 23:55:00. How do I select all the records from a table that have been updated between these dates. I have converted the 2 times to seconds in the Unix script prior to issuing the psql command, and have calculated the interval in seconds between the 2 periods.
I thought something like
SELECT A,B,C FROM table
WHERE xtime BETWEEN now() - interval '$selectedtimeParm(in secs)' AND now();
I am having trouble evaluating the Parm for the selectedtimeParm - it doesn't resolve properly.
Editor's note: I did not change the inaccurate use of the terms period, time frame, time and date for the datetime type timestamp because I discuss that in my answer.
What's wrong with:
SELECT a,b,c
FROM table
WHERE xtime BETWEEN '2012-04-01 23:55:00'::timestamp
AND now()::timestamp;
If you want to operate with a count of seconds as interval:
...
WHERE xtime BETWEEN now()::timestamp - (interval '1s') * $selectedtimeParm
AND now()::timestamp;
Note the standard ISO 8601 date format YYYY-MM-DD h24:mi:ss which is unambiguous with any locale or DateStyle setting.
The first value for the BETWEEN construct must be the smaller one. If you don't know which value is smaller use BETWEEN SYMMETRIC instead.
In your question you refer to the datetime type timestamp as "date", "time" and "period". In the title you used the term "time frames", which I changed to "timestamps". All of these terms are wrong. Freely interchanging them makes the question even harder to understand.
That, and the fact that you only tagged the question psql (the problem hardly concerns the command line terminal) might help to explain why nobody answered for days. Normally, it's a matter of minutes around here. I had a hard time understanding your question.
Understand the data types date, interval, time and timestamp - with or without time zone. Start by reading the chapter "Date/Time Types" in the manual.
Error message would have gone a long way, too.
For anyone who is looking for the fix to this. You need to remove timestamp from the where clause and use BETWEEN!
TABLENAME.COL-NAME-FOR-TIMESTAMP BETWEEN '2020-01-29 04:18:00-06' AND CURRENT_TIMESTAMP