[BUGS] Re: [BUGS] Return value error of‘to_timestamp’

[David G. Johnston]

When the fractional seconds more than 6, the return value of to_timestamp
without truncation.
Postgres think the total value of the.123456789 as a fractional second
part and convert to microsecond stored in database.
postgres=# select to_timestamp('1990-1-1 11:11:11.123456789', 'YYYY-MM-DD
HH24:MI:SS.US');
to_timestamp
-------------------------------
1990-01-01 11:13:14.456789+08
(1 row)
postgres=#

​Working as designed...​its suggested to use data type casting whenever
possible to avoid this issue.

​https://www.postgresql.org/docs/9.6/static/functions-formatting.html

​"""
to_timestamp and to_date exist to handle input formats that cannot be
converted by simple casting. These functions interpret input liberally,
with minimal error checking. While they produce valid output, the
conversion can yield unexpected results. For example, input to these
functions is not restricted by normal ranges, thus
to_date('20096040','YYYYMMDD') returns 2014-01-17 rather than causing an
error. Casting does not have this behavior.
​"""​
​
This may also be relevant...I'm not personally familiar with the usage of
this function​.

"""
In a conversion from string to timestamp, millisecond (MS) or microsecond
(US) values are used as the seconds digits after the decimal point. For
example to_timestamp('12:3', 'SS:MS') is not 3 milliseconds, but 300,
because the conversion counts it as 12 + 0.3 seconds. This means for the
format SS:MS, the input values 12:3, 12:30, and 12:300 specify the same
number of milliseconds. To get three milliseconds, one must use 12:003,
which the conversion counts as 12 + 0.003 = 12.003 seconds.

Here is a more complex example: to_timestamp('15:12:02.020.001230', 'HH:MI:
SS.MS.US') is 15 hours, 12 minutes, and 2 seconds + 20 milliseconds + 1230
microseconds = 2.021230 seconds.
"""

David J.

[Aleksander Alekseev]

postgres=# select to_timestamp('1990-1-1 11:11:11.123456789',
'YYYY-MM-DD HH24:MI:SS.US'); to_timestamp
-------------------------------
1990-01-01 11:13:14.456789+08
(1 row)
postgres=#

​Working as designed...​

Maybe it means that current design is poor. However since this behavior
is documented there are users who might depend on it. So I doubt it
will be changed any time soon.

Though I wonder maybe we should consider introducing a new set of
time-related procedures with different behavior (to_timestamp_strict?),
that would be more obvious to users.