Thread

1. to_timestamp function calculation error

   myzhen <zhenmingyang@yeah.net> — 2024-12-17T11:51:44Z

   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

2. Re: to_timestamp function calculation error

   Tom Lane <tgl@sss.pgh.pa.us> — 2024-12-17T15:31:50Z

   myzhen <zhenmingyang@yeah.net> writes:
   > 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.
   
   I believe this is intentional.
   
   			regards, tom lane