so, does this overlap or not...? - fencepost question on overlaps()
Hi,
This doesn't seem to make sense to me, can someone explain the rationale
behind it?
postgres=# select version();
version
---------------------------------------------------------------------------------------
PostgreSQL 8.4.4 on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC)
4.3.3, 64-bit
(1 row)
Range 1 ending on date A does not overlap with range 2 starting on date A:
postgres=# select ('2010-01-01'::date, '2010-01-05'::date) overlaps
('2010-01-05'::date, '2010-01-10'::date);
overlaps
----------
f
(1 row)
But it does when range 1 is only a single day:
postgres=# select ('2010-01-05'::date, '2010-01-05'::date) overlaps
('2010-01-05'::date, '2010-01-10'::date);
overlaps
----------
t
(1 row)
BTW, it doesn't matter whether one casts to date or timestamp
--
Best,
Frank.
Frank van Vugt <ftm.van.vugt@foxi.nl> writes:
This doesn't seem to make sense to me, can someone explain the rationale
behind it?
The rationale is "do what the SQL spec says" ;-)
What the spec says is
( S1 > S2 AND NOT ( S1 >= T2 AND T1 >= T2 ) )
OR
( S2 > S1 AND NOT ( S2 >= T1 AND T2 >= T1 ) )
OR
( S1 = S2 AND ( T1 <> T2 OR T1 = T2 ) )
I seem to recall a previous discussion in the PG lists where we
reverse-engineered a plausible explanation of what the standards
committee had in mind when they wrote this, but I don't have time
right now to go looking for it.
regards, tom lane
Hi Tom,
The rationale is "do what the SQL spec says" ;-)
can't argue with the standard ;)
I seem to recall a previous discussion in the PG lists
Good memory !
Adding 'sql standard' to the search options helped, this issue seems to elude
people every now and then, given (amongst others):
http://archives.postgresql.org/pgsql-hackers/2005-05/msg01457.php
http://archives.postgresql.org/pgsql-general/2006-11/msg00763.php
http://archives.postgresql.org/pgsql-general/2006-11/msg00527.php
One might consider adding a single line to the end of 9.9 of the docs that
warns for this behaviour and/or add the specific example....?
Thanks for your help.
--
Best,
Frank.
Frank van Vugt <ftm.van.vugt@foxi.nl> writes:
One might consider adding a single line to the end of 9.9 of the docs that
warns for this behaviour and/or add the specific example....?
I put some more explanation and examples into the 9.0 docs:
http://developer.postgresql.org/pgdocs/postgres/functions-datetime.html
regards, tom lane