When calling the to_timestamp function, if the actual parameter passed is a negative year and you specify BC, this will cause to_timestamp to return an AD date.
example：select to_timestamp('-2011-2-18 15:13:14 BC', 'YYYY-MM-DD HH24:MI:SS BC');
I tested is as follows:
postgres=# select to_timestamp('-2011-2-18 15:13:14', 'YYYY-MM-DD HH24:MI:SS BC');
to_timestamp
---------------------------------
2011-02-18 15:13:14+08:05:43 BC
(1 row)
postgres=# select to_timestamp('-2011-2-18 15:13:14 BC', 'YYYY-MM-DD HH24:MI:SS BC');
to_timestamp
------------------------
2011-02-18 15:13:14+08
(1 row)
postgres=# select to_timestamp('-2011-2-18 15:13:14 BC', 'YYYY-MM-DD HH24:MI:SS BC') = to_timestamp('2011-2-18 15:13:14', 'YYYY-MM-DD HH24:MI:SS');
?column?
----------
t
(1 row)
postgres=#
I found the following code snippet in do_to_timestamp function:
{
/* If a 4-digit year is provided, we use that and ignore CC. */
tm->tm_year = tmfc.year;
if (tmfc.bc)
tm->tm_year = -tm->tm_year;
/* correct for our representation of BC years */
if (tm->tm_year < 0)
tm->tm_year++;
}
As long as tmfc.bc is true, tm->tm_year = tm->tm_year * -1, that's what led to this scene.
I haven't tested on other DBMS so I'm not sure if that's an issue.
Best regards
