Thread: Help with date math

I need some help.  I am trying to replicate a function from Sybase ASA, and am having difficulty.

I need to be able to subtract 2 date (or timestamps) and return the results expressed in days, weeks, month, quarters, or years.  How do I do this?

I believe Postgres is returning the number of days when you subtract to days.
i.e. postgres=# select current_date - '2007/01/01';
 ?column?
----------
      200
(1 row)



However, I can not figure out how to get the results expressed as 7 months, or 2 quarters, x weeks, or 0 years.  I have tried to use date_part, but since the subtraction is returning an integer, it is not happy.

Any help would be greatly appreciated.

Chris

P.S.

I'm trying to replicate Sybase's datediff function.

Chris Hoover wrote:
> I need some help.  I am trying to replicate a function from Sybase
> ASA, and am having difficulty.
>
> I need to be able to subtract 2 date (or timestamps) and return the
> results expressed in days, weeks, month, quarters, or years.  How do I
> do this?
>
> I believe Postgres is returning the number of days when you subtract
> to days.
> i.e. postgres=# select current_date - '2007/01/01';
>  ?column?
> ----------
>       200
> (1 row)
>
>
>
> However, I can not figure out how to get the results expressed as 7
> months, or 2 quarters, x weeks, or 0 years.  I have tried to use
> date_part, but since the subtraction is returning an integer, it is
> not happy.
>
> Any help would be greatly appreciated.
>
> Chris
>
> P.S.
>
> I'm trying to replicate Sybase's datediff function.
postgres=# select age(current_date,'2007/01/01');
      age
----------------
 6 mons 20 days
(1 row)


http://www.postgresql.org/docs/8.2/static/functions-datetime.html

Chris Hoover wrote:
> I need some help.  I am trying to replicate a function from Sybase
> ASA, and am having difficulty.
>
> I need to be able to subtract 2 date (or timestamps) and return the
> results expressed in days, weeks, month, quarters, or years.  How do I
> do this?
>
> I believe Postgres is returning the number of days when you subtract
> to days.
> i.e. postgres=# select current_date - '2007/01/01';
>  ?column?
> ----------
>       200
> (1 row)
>
>
>
> However, I can not figure out how to get the results expressed as 7
> months, or 2 quarters, x weeks, or 0 years.  I have tried to use
> date_part, but since the subtraction is returning an integer, it is
> not happy.
>
> Any help would be greatly appreciated.
>
> Chris
>
> P.S.
>
> I'm trying to replicate Sybase's datediff function.
postgres=# select date_part('month', age(current_date, '2007/01/01'));
 date_part
-----------
         6
(1 row)

On fös, 2007-07-20 at 11:08 -0400, Chris Hoover wrote:
> I need some help.  I am trying to replicate a function from Sybase
> ASA, and am having difficulty.
>
> I need to be able to subtract 2 date (or timestamps) and return the
> results expressed in days, weeks, month, quarters, or years.  How do I
> do this?
>
> I believe Postgres is returning the number of days when you subtract
> to days.

>
> However, I can not figure out how to get the results expressed as 7
> months,
  would not 6 months be more logical?

>  or 2 quarters, x weeks, or 0 years.

have you tried to use extract() ?

there is an old compatibility project on pgfoundry that has a
datediff function, but i have no idea how well it copies the
mssql behaviour.

http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/mssqlsupport/datetimefunctions.sql?rev=1.1.1.1&content-type=text/x-cvsweb-markup

it looks a bit simplistic to me, but maybe that is exactly what
you need.

gnari