Re: [GENERAL] '1 year' = '360 days' ????
Guy Fraser wrote: Trivia: In approximately 620 million years a day will be twice as long as it is today. Do you think then that Postgres628M.0 will fix it ? :-) Regards Gaetano Mendola ---(end of broadcast)--- TIP 8: explain analyze is your friend
Re: [GENERAL] '1 year' = '360 days' ????
Gaetano Mendola wrote: Guy Fraser wrote: Trivia: In approximately 620 million years a day will be twice as long as it is today. Do you think then that Postgres628M.0 will fix it ? :-) Regards Gaetano Mendola I just hope, I don't have to work an equivalent fraction of the day for the same pay, but with any luck I'll have all my bills paid and be retired by then. ;-) -- Guy Fraser Network Administrator The Internet Centre 780-450-6787 , 1-888-450-6787 There is a fine line between genius and lunacy, fear not, walk the line with pride. Not all things will end up as you wanted, but you will certainly discover things the meek and timid will miss out on. ---(end of broadcast)--- TIP 6: Have you searched our list archives? http://archives.postgresql.org
Re: [GENERAL] '1 year' = '360 days' ????
On Wed, Oct 27, 2004 at 16:26:13 -0600, Guy Fraser [EMAIL PROTECTED] wrote: When calculating any usage based on time, it is a good idea to store usage in days:hours:minutes:seconds because they are static and stable, if you discount the deceleration of the earth and corrections in leap seconds for atomic clocks [see http://tycho.usno.navy.mil/leapsec.html ]. The length of calendar days isn't constant. In many timezones, one day a year is 23 hours long and another is 25 hours long. Having month and year intervals is useful for events that repeat monthly or yearly in spite of there not being a constant number of seconds between events. ---(end of broadcast)--- TIP 2: you can get off all lists at once with the unregister command (send unregister YourEmailAddressHere to [EMAIL PROTECTED])
Re: [GENERAL] '1 year' = '360 days' ????
Tom Lane wrote: Doug McNaught [EMAIL PROTECTED] writes: template1=# select '1 year'::interval = '360 days'::interval; ?column? -- t (1 row) Yeah, if you look at interval_cmp_internal() it's fairly obvious why. I think that this definition is probably bogus, and that only intervals that match exactly (equal months parts *and* equal seconds parts) should be considered equal. However the most obvious way to redefine it (compare the months, and only if equal compare the seconds) would lead to rather nonintuitive behaviors such as '1 year' '1000 days'. Anybody have any thoughts about a better way to map the multicomponent reality into a one-dimensional sorting order? (Note also that as Bruno was just mentioning, we really ought to have months/days/seconds components, not just months/seconds; which makes the comparison issue even more interesting.) regards, tom lane As any of us who have ever researched how to calculate time know; 1) The amount of time in 1 year depends on the year due to leap years. 2) The amount of time in 1 month depends on the month and year because a month is an arbitrary number of days. 3) A week is a theological creation always equal to 7 days. Using the Gregorian Calendar there are 10 missing days between Oct. 4, 1582 and Oct. 15, 1582 . Leap Years are (((every 4 years) except when modulo 100) except when modulo 400). It is therefore not possible to define a Month or Year in Seconds, without knowing which Day, Month and Year you calculating. Time constants : 1 Solar Day = 23 hours 56 minutes 4.091 seconds 1 Lunar Month = 27.32158 days 1 Tropical Year = 365.24215 Solar Days 1 Year in Gregorian time is : 365 Days 5 Hours 49 Minutes 12 Seconds As it is now obvious there is not any simple way to convert months to seconds since a month is an abstract number of days used to split four (13 week) seasons three ways plus one day every non leap year and two days every leap year. When calculating any usage based on time, it is a good idea to store usage in days:hours:minutes:seconds because they are static and stable, if you discount the deceleration of the earth and corrections in leap seconds for atomic clocks [see http://tycho.usno.navy.mil/leapsec.html ]. Trivia: In approximately 620 million years a day will be twice as long as it is today. -- Guy Fraser Network Administrator The Internet Centre 780-450-6787 , 1-888-450-6787 There is a fine line between genius and lunacy, fear not, walk the line with pride. Not all things will end up as you wanted, but you will certainly discover things the meek and timid will miss out on. ---(end of broadcast)--- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]
Re: [GENERAL] '1 year' = '360 days' ????
Tom Lane wrote: Bruno Wolff III [EMAIL PROTECTED] writes: Wikipedia gives 365.242189670 days (86400 seconds) as the length of the mean solar year in 2000. To give you some idea of how constant that values is, Wikipedia claims that 2000 years ago the mean solar year was about 10 seconds longer. Using the above value I get there is an average of 2629743 seconds in a month. And yet another option is to note that in the Gregorian calendar there are 400*365+97 days or 400*12 months in 400 years, which gives 2629746 seconds per month on average. I like the latter approach, mainly because it gives a defensible rationale for using a particular exact value. With the solar-year approach there's no strong reason why you should use 2000 (or any other particular year) as the reference; and any value you did use would be subject to both roundoff and observational error. With the Gregorian calendar as reference, 2629746 seconds is the *exact* answer, and it's correct because the Pope says so ;-). (Or, for the Protestants among us, it's correct because the SQL standard specifies use of the Gregorian calendar.) regards, tom lane Give or take one day every 4000 years. ;-) -- Guy Fraser Network Administrator The Internet Centre 780-450-6787 , 1-888-450-6787 There is a fine line between genius and lunacy, fear not, walk the line with pride. Not all things will end up as you wanted, but you will certainly discover things the meek and timid will miss out on. ---(end of broadcast)--- TIP 2: you can get off all lists at once with the unregister command (send unregister YourEmailAddressHere to [EMAIL PROTECTED])
Re: [GENERAL] '1 year' = '360 days' ????
problem is that '1 months':: interval does not have the same value if you add it to a date or another : = SELECT '2004-02-01'::timestamp+'1 month'::interval, '2004-03-01'::timestamp+'1 month'::interval; ?column? | ?column? -+- 2004-03-01 00:00:00 | 2004-04-01 00:00:00 SELECT '2004-03-01'::timestamp-'2004-02-01'::timestamp, '2004-04-01'::timestamp-'2004-03-01'::timestamp; ?column? | ?column? --+-- 29 days | 31 days That's because a month is an undefined number of days (also some years are 366 days). In that case '1 months':: interval is either 29 or 31 days but it could be 28 in february 2003 or 30 in april ! Thus if we have a date d and two intervals i1 and i2 : The comparison (d+i1) (d+i2) depends on the value of d (and the timezone). For instance if i1 is '1 month' and i2 is '30 days', we have : SELECT '2004-02-01'::timestamp+'1 month'::interval, '2004-02-01'::timestamp+'30 days'::interval; ?column? | ?column? -+- 2004-03-01 00:00:00 | 2004-03-02 00:00:00 Thus (d+i1) (d+i2) SELECT '2004-04-01'::timestamp+'1 month'::interval, '2004-04-01'::timestamp+'30 days'::interval; ?column? | ?column? -+- 2004-05-01 00:00:00 | 2004-05-01 00:00:00 Thus (d+i1) = (d+i2) SELECT '2004-03-01'::timestamp+'1 month'::interval, '2004-03-01'::timestamp+'30 days'::interval; ?column? | ?column? -+- 2004-04-01 00:00:00 | 2004-03-31 00:00:00 Thus (d+i1) (d+i2) And that's normal ! Intervals having months are extremely useful to express the idea of 'same day, next month' that you can't do with just an interval expressed in seconds. However, beware : SELECT '2004-01-31'::timestamp+'1 month'::interval; ?column? - 2004-02-29 00:00:00 (1 ligne) SELECT '2004-01-30'::timestamp+'1 month'::interval; ?column? - 2004-02-29 00:00:00 (1 ligne) SELECT '2004-01-29'::timestamp+'1 month'::interval; ?column? - 2004-02-29 00:00:00 (1 ligne) SELECT '2004-01-28'::timestamp+'1 month'::interval; ?column? - 2004-02-28 00:00:00 31 january + 1 month = 29 february (it clips at the end of the month, which is IMHO GOOD). How can we sort intervals meaningfully in these conditions ? Can we ? In fact the value of an interval depends on the application, and intervals with months are in another 'world' than intervals with only seconds... same thing for years. ---(end of broadcast)--- TIP 6: Have you searched our list archives? http://archives.postgresql.org ---(end of broadcast)--- TIP 6: Have you searched our list archives? http://archives.postgresql.org
Re: [GENERAL] '1 year' = '360 days' ????
On Oct 24, 2004, at 4:13 PM, Pierre-Frédéric Caillaud wrote: How can we sort intervals meaningfully in these conditions ? Can we ? In fact the value of an interval depends on the application, and intervals with months are in another 'world' than intervals with only seconds... same thing for years. Added to this, I've been wondering whether '1 day'::interval is also problematic wrt daylight savings time or changing time zones. The whole thing seems pretty hairy to me. Michael Glaesemann grzm myrealbox com ---(end of broadcast)--- TIP 9: the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [GENERAL] '1 year' = '360 days' ????
Michael Glaesemann [EMAIL PROTECTED] writes: Added to this, I've been wondering whether '1 day'::interval is also problematic wrt daylight savings time or changing time zones. This is exactly the point I alluded to earlier: intervals need to have three components (months, days, seconds) not just two. That's been on the to-do list for quite awhile. All the other units we support for intervals bear a fixed relationship to one or another of these, so three is sufficient. Question to think about: should we allow fractional months or days in the stored representation? There are some places where the existing restriction that the months field is an integer requires awkward compromises. On the other hand, it's not real clear what a fractional month actually means, and similarly a fractional day is hard to assign meaning to without positing that 1 day == 24 hours. regards, tom lane ---(end of broadcast)--- TIP 4: Don't 'kill -9' the postmaster
Re: [GENERAL] '1 year' = '360 days' ????
On Sun, Oct 24, 2004 at 11:29:13 -0400, Tom Lane [EMAIL PROTECTED] wrote: Question to think about: should we allow fractional months or days in the stored representation? There are some places where the existing restriction that the months field is an integer requires awkward compromises. On the other hand, it's not real clear what a fractional month actually means, and similarly a fractional day is hard to assign meaning to without positing that 1 day == 24 hours. There are reasonable addition and subtraction operation definitions on two intervals. There might be some application where you want to keep track of fractional months or days. What I am not sure of is would you really have a reason to add fractional months or days to a timestamp. There are a couple reasonable definitions you might make for this definition, but I don't really see a good reason to want this. ne thing to note, when adding intervals you can add the fractions normally. When adding to a date you can get the actual length of the day or month the fractional part adds to, if you wanted to use that information. (Though the resulting day or month may not be the one you added the fractional month to.) I think starting with a type where months and days were integers would be OK, since you could generalize it to handle fractional months and days later and not break applications. Another thing to think about when designing this type, is that when adding timestamps and intervals it makes a difference in which order you add the months, days and seconds. ---(end of broadcast)--- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [GENERAL] '1 year' = '360 days' ????
Bruno Wolff III [EMAIL PROTECTED] writes: Wikipedia gives 365.242189670 days (86400 seconds) as the length of the mean solar year in 2000. To give you some idea of how constant that values is, Wikipedia claims that 2000 years ago the mean solar year was about 10 seconds longer. Using the above value I get there is an average of 2629743 seconds in a month. And yet another option is to note that in the Gregorian calendar there are 400*365+97 days or 400*12 months in 400 years, which gives 2629746 seconds per month on average. I like the latter approach, mainly because it gives a defensible rationale for using a particular exact value. With the solar-year approach there's no strong reason why you should use 2000 (or any other particular year) as the reference; and any value you did use would be subject to both roundoff and observational error. With the Gregorian calendar as reference, 2629746 seconds is the *exact* answer, and it's correct because the Pope says so ;-). (Or, for the Protestants among us, it's correct because the SQL standard specifies use of the Gregorian calendar.) regards, tom lane ---(end of broadcast)--- TIP 4: Don't 'kill -9' the postmaster
Re: [GENERAL] '1 year' = '360 days' ????
From: Tom Lane [EMAIL PROTECTED] To: Ricardo Perez Lopez [EMAIL PROTECTED] CC: [EMAIL PROTECTED] Subject: Re: [GENERAL] '1 year' = '360 days' Date: Sat, 23 Oct 2004 19:52:50 -0400 Ricardo Perez Lopez [EMAIL PROTECTED] writes: I have observed that, for PostgreSQL, one year is actually 360 days: SELECT '1 year'::timestamp = '360 days'::timestamp; ?column? - t Nonsense. regression=# SELECT '1 year'::timestamp = '360 days'::timestamp; ERROR: invalid input syntax for type timestamp: 1 year How about telling us what you *really* did, instead of posting faked examples? Sorry: it's an errata. The query is, actually: SELECT '1 year'::interval = '360 days'::interval; Sorry about the inconvenience. There are some contexts in which an interval (not a timestamp) of 1 month will be taken as equivalent to 30 days, for lack of any better idea, but it's not the case that Postgres doesn't know the difference. regards, tom lane Thanks. _ Acepta el reto MSN Premium: Protección para tus hijos en internet. Descárgalo y pruébalo 2 meses gratis. http://join.msn.com?XAPID=1697DI=1055HL=Footer_mailsenviados_proteccioninfantil ---(end of broadcast)--- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
[GENERAL] '1 year' = '360 days' ????
Hello everyone:
I'm a PostgreSQL newbie, working now with dates, times, timestamps and
intervals.
I have three questions about the above:
FIRST:
I have observed that, for PostgreSQL, one year is actually 360 days:
SELECT '1 year'::timestamp = '360 days'::timestamp;
?column?
-
t
Glubs! I believed that 1 year is 365 days, or 366 if leap. Is it normal?
SECOND:
---
When I want to check how many time is between two dates, I have two options
(which shows two different results):
SELECT '30-09-04'::timestamp - '30-09-03'::timestamp,
age('30-09-04'::timestamp, '30-09-03'::timestamp);
?column? |age
---
@ 366 days | @ 1 year
The results are different. If we compare the two results:
SELECT ('30-09-04'::timestamp - '30-09-03'::timestamp) =
age('30-09-04'::timestamp, '30-09-03'::timestamp);
?column?
--
f
Obviously, it returns False, because I told in the first question, 1 year is
360 days for PostgreSQL.
The question is: is it normal? Which of the two methods is the correct? To
substract timestamps? Or to use the age function?
THIRD:
As I told in the second question, when I do:
SELECT '30-09-04'::timestamp - '30-09-03'::timestamp;
the result is:
?column?
--
@ 366 days
The question is: is there any way to normalize the result, such that the
result was:
@ 1 year 1 day
?
I think it's better (and more correct) @ 1 year 1 day rather than @ 366
days. Is there any way to achieve that?
Thanks to all.
Ricardo.
_
Horóscopo, tarot, numerología... Escucha lo que te dicen los astros.
http://astrocentro.msn.es/
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Re: [GENERAL] '1 year' = '360 days' ????
Ricardo Perez Lopez [EMAIL PROTECTED] writes: I have observed that, for PostgreSQL, one year is actually 360 days: SELECT '1 year'::timestamp = '360 days'::timestamp; ?column? - t Nonsense. regression=# SELECT '1 year'::timestamp = '360 days'::timestamp; ERROR: invalid input syntax for type timestamp: 1 year How about telling us what you *really* did, instead of posting faked examples? There are some contexts in which an interval (not a timestamp) of 1 month will be taken as equivalent to 30 days, for lack of any better idea, but it's not the case that Postgres doesn't know the difference. regards, tom lane ---(end of broadcast)--- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faqs/FAQ.html
Re: [GENERAL] '1 year' = '360 days' ????
Tom Lane [EMAIL PROTECTED] writes: Ricardo Perez Lopez [EMAIL PROTECTED] writes: I have observed that, for PostgreSQL, one year is actually 360 days: SELECT '1 year'::timestamp = '360 days'::timestamp; ?column? - t Nonsense. regression=# SELECT '1 year'::timestamp = '360 days'::timestamp; ERROR: invalid input syntax for type timestamp: 1 year How about telling us what you *really* did, instead of posting faked examples? FWIW: template1=# select '1 year'::interval = '360 days'::interval; ?column? -- t (1 row) template1=# select '1 year'::interval = '365 days'::interval; ?column? -- f (1 row) template1=# select version(); version - PostgreSQL 7.4.5 on i686-pc-linux-gnu, compiled by GCC egcs-2.91.66 (1 row) -Doug ---(end of broadcast)--- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [GENERAL] '1 year' = '360 days' ????
Doug McNaught [EMAIL PROTECTED] writes: template1=# select '1 year'::interval = '360 days'::interval; ?column? -- t (1 row) Yeah, if you look at interval_cmp_internal() it's fairly obvious why. I think that this definition is probably bogus, and that only intervals that match exactly (equal months parts *and* equal seconds parts) should be considered equal. However the most obvious way to redefine it (compare the months, and only if equal compare the seconds) would lead to rather nonintuitive behaviors such as '1 year' '1000 days'. Anybody have any thoughts about a better way to map the multicomponent reality into a one-dimensional sorting order? (Note also that as Bruno was just mentioning, we really ought to have months/days/seconds components, not just months/seconds; which makes the comparison issue even more interesting.) regards, tom lane ---(end of broadcast)--- TIP 2: you can get off all lists at once with the unregister command (send unregister YourEmailAddressHere to [EMAIL PROTECTED])
Re: [GENERAL] '1 year' = '360 days' ????
On Sat, Oct 23, 2004 at 21:38:15 -0400, Tom Lane [EMAIL PROTECTED] wrote: Doug McNaught [EMAIL PROTECTED] writes: template1=# select '1 year'::interval = '360 days'::interval; ?column? -- t (1 row) Yeah, if you look at interval_cmp_internal() it's fairly obvious why. I think that this definition is probably bogus, and that only intervals that match exactly (equal months parts *and* equal seconds parts) should be considered equal. However the most obvious way to redefine it (compare the months, and only if equal compare the seconds) would lead to rather nonintuitive behaviors such as '1 year' '1000 days'. Anybody have any thoughts about a better way to map the multicomponent reality into a one-dimensional sorting order? You could return NULL for cases where the number of months in the first interval is less than the second, but the number of seconds in the second interval is greater than the first. You could even tighten things down more by using that months have to be at least 28 days, but not more than 31 days (neglecting daylight savings time). If you want to be able to use a btree index, you need a total ordering, so in that case I think you have to have things work pretty much the way they do now, including the way the equality operator works. ---(end of broadcast)--- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]
Re: [GENERAL] '1 year' = '360 days' ????
Bruno Wolff III [EMAIL PROTECTED] writes: Tom Lane [EMAIL PROTECTED] wrote: Anybody have any thoughts about a better way to map the multicomponent reality into a one-dimensional sorting order? You could return NULL for cases where the number of months in the first interval is less than the second, but the number of seconds in the second interval is greater than the first. No, you can't, at least not if you want to have btree indexes on interval columns. The comparison operators can never return NULL for nonnull inputs. If you want to be able to use a btree index, you need a total ordering, so in that case I think you have to have things work pretty much the way they do now, including the way the equality operator works. We don't have to have this particular sorting decision, we just have to have *some* unique sorting order. In particular, if we want to say that two interval values are not equal, we have to be able to say which one is less. For instance, compare the months first and only if equal compare the seconds would work fine from the point of view of btree. It's just that that leads to a sort order that users will probably not like very much. regards, tom lane ---(end of broadcast)--- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faqs/FAQ.html
Re: [GENERAL] '1 year' = '360 days' ????
On Sat, Oct 23, 2004 at 23:36:05 -0400, Tom Lane [EMAIL PROTECTED] wrote: We don't have to have this particular sorting decision, we just have to have *some* unique sorting order. In particular, if we want to say that two interval values are not equal, we have to be able to say which one is less. For instance, compare the months first and only if equal compare the seconds would work fine from the point of view of btree. It's just that that leads to a sort order that users will probably not like very much. One way to do comparisons is to use a mapping f(m,s) = R and compare (m1,s1) and (m2,s2) by comparing f(m1,s1) and f(m2,s2) and break ties by comparing say m1 and m2. This will work as long as f(m,s1) = f(m,s2) implies s1 = s2. It will probably be desirable to use a subset of these mappings where f(m,s) = g(m) + h(s). In fact the current system uses this with g(m) = 30*24*60*60*m and h(s) = s (but without the tiebreak that compares m values). Because of the way intervals work, I think you want to use an ordering generated like that you want to use something of the form f(m,s) = C1*m + C2*s. I also think that treating a month as 30 days and having round numbers is better than using something like 1/12 a solar year in seconds. So I think the best plan is to do things as they are now, except for adding a tie breaker just using months or seconds for when both intervals give the same number of seconds when treating months as 30 days, but have a different number of months. ---(end of broadcast)--- TIP 9: the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [GENERAL] '1 year' = '360 days' ????
On Sat, Oct 23, 2004 at 23:15:57 -0500, Bruno Wolff III [EMAIL PROTECTED] wrote: by comparing say m1 and m2. This will work as long as f(m,s1) = f(m,s2) implies s1 = s2. It will probably be desirable to use a subset of these mappings where f(m,s) = g(m) + h(s). In fact the current system uses this with g(m) = 30*24*60*60*m and h(s) = s (but without the tiebreak that compares m values). Because of the way intervals work, I think you want to use an ordering generated like that you want to use something of the form f(m,s) = C1*m + C2*s. I also think that treating a month as 30 days and having round numbers is better than using something like 1/12 a solar year in seconds. So I think the best plan is to do things as they are now, except for adding a tie breaker just using months or seconds for when both intervals give the same number of seconds when treating months as 30 days, but have a different number of months. Some more comments on this. I was thinking about it a bit more and using 1/12 of the number of seconds in a solar year doesn't seem that bad for comparisons. That way 366 days 1 year 365 days. However, if you go that route, I think you would also want to change EXTRACT so that when you extract the EPOCH you use the same function as for comparison. One value I found for a solar year is 365 days, 5 hours, 48 minutes, 45.51 seconds. ---(end of broadcast)--- TIP 4: Don't 'kill -9' the postmaster
Re: [GENERAL] '1 year' = '360 days' ????
On Sat, Oct 23, 2004 at 23:51:20 -0500, Bruno Wolff III [EMAIL PROTECTED] wrote: One value I found for a solar year is 365 days, 5 hours, 48 minutes, 45.51 seconds. Wikipedia gives 365.242189670 days (86400 seconds) as the length of the mean solar year in 2000. To give you some idea of how constant that values is, Wikipedia claims that 2000 years ago the mean solar year was about 10 seconds longer. Using the above value I get there is an average of 2629743 seconds in a month. And yet another option is to note that in the Gregorian calendar there are 400*365+97 days or 400*12 months in 400 years, which gives 2629746 seconds per month on average. ---(end of broadcast)--- TIP 6: Have you searched our list archives? http://archives.postgresql.org
