Tom Lane wrote: > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > OK, I have a new patch, which simplifies the code by using > > TrimTrailingZeros(), gives more consistent subsecond display, and > > subpresses the rounding problem: > > Does anyone have any idea why the existing code is designed to keep the > number of displayed fractional digits even? It seems a bit silly to > me too, but we probably ought not remove what was clearly an intentional > behavior without understanding why it was intentional.
If you look at TrimTrailingZeros(), you will see it keeps at least two decimal digits of display, so I suppose the special case while() loop was just an older version of that. I can't imagine why they would only want even digits, but given the other weird things in the datetime code, it isn't surprising. > Also, I will point out once more that the problem is not "we only have > nine digits of precision not ten". The problem is that the precision > degrades as the interval gets larger. > > regression=# select '20 days 15 hours 57 mins 12.1 secs ago'::interval; > interval > ------------------------------- > -20 days -15:57:12.1000000001 > (1 row) > > regression=# select '100020 days 15 hours 57 mins 12.1 secs ago'::interval; > interval > ----------------------------------- > -100020 days -15:57:12.1000003815 > (1 row) > > regression=# select '100000020 days 15 hours 57 mins 12.1 secs ago'::interval; > interval > ------------------------------------- > -100000020 days -15:57:12.099609375 > (1 row) > > regression=# > > Without accounting for that fundamental fact, you will not have a > solution, only a kluge. Yep, it just hits the most common complaint for <30 days --- larger values are going to round funny. I can't think of how to round it cleanly without adding a lot of hacky code dealing with floats and exponents. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(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
