On Tue, Mar 24, 2015 at 03:08:26PM -0400, Bruce Momjian wrote: > On Tue, Mar 24, 2015 at 10:05:12AM -0400, Bruce Momjian wrote: > > On Tue, Mar 24, 2015 at 09:47:56AM -0400, Noah Misch wrote: > > > On Sun, Mar 22, 2015 at 10:53:12PM -0400, Bruce Momjian wrote: > > > > On Sun, Mar 22, 2015 at 04:41:19PM -0400, Noah Misch wrote: > > > > > On Wed, Mar 18, 2015 at 05:52:44PM -0400, Bruce Momjian wrote: > > > > > > This "junk" digit zeroing matches the Oracle behavior: > > > > > > > > > > > > SELECT to_char(1.123456789123456789123456789d, > > > > > > '9.9999999999999999999999999999999999999') as x from dual; > > > > > > ------ > > > > > > 1.1234567891234568000000000000000000000 > > > > > > > > > > > > Our output with the patch would be: > > > > > > > > > > > > SELECT to_char(float8 '1.123456789123456789123456789', > > > > > > '9.9999999999999999999999999999999999999'); > > > > > > ------ > > > > > > 1.1234567891234500000000000000000000000 > > > > > > > > These outputs show Oracle treating 17 digits as significant while > > > > > PostgreSQL > > > > > treats 15 digits as significant. Should we match Oracle in this > > > > > respect while > > > > > we're breaking compatibility anyway? I tend to think yes. > > > > > > > > Uh, I am hesistant to adjust our precision to match Oracle as I don't > > > > know what they are using internally. > > > > > > http://sqlfiddle.com/#!4/8b4cf/5 strongly implies 17 significant digits > > > for > > > float8 and 9 digits for float4. > > > > OK, I am fine in using those values if you can find them as compiler > > defines, but I don't see how we can grab those values from a user test > > on Oracle.
We encounter no authority higher than the test results, so it would be wrong to seek out and use a define that just happens to match a test result. Adding "#define TO_CHAR_DBL_DIG 17" and "#define TO_CHAR_FLT_DIG 9" is good. > > There are some "invisible" float digits that don't appear in %f but can > > be shown if desired --- I think we used to do that in the regression > > tests, but found they added too much platform-specific randomness. Do > > we want to go in that direction? Bare %f simply prints all digits before the decimal point and exactly six digits after the decimal point. Whether implementation-defined digits appear in that output depends on the number's magnitude. However, float8out and float4out do behave along the lines of your description. I do recommend pushing TO_CHAR in that direction, to make it more like Oracle while we're already breaking compatibility with PostgreSQL 9.4. > How about if we have to_char() honor our extra_float_digits GUC, so > users who want those digits can get them? It's not my first choice; for one thing, no value of extra_float_digits would yield 17 digits for float8 and 9 digits for float4. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
