[Pypgsql-devel] [ pypgsql-Bugs-800801 ] Precision lost from mxDateTime during queries

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Bugs item #800801, was opened at 2003-09-05 02:17
Message generated for change (Settings changed) made by ghaering
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Category: PgSQL
Group: None
Status: Open
Resolution: Accepted
Priority: 5
Private: No
Submitted By: Mike C. Fletcher (mcfletch)
>Assigned to: Nobody/Anonymous (nobody)
Summary: Precision lost from mxDateTime during queries

Initial Comment:
When working with PostgreSQL timestamps, round-trips
to/from Python wind up losing data (the
least-significant digits of the timestamp, 1000ths of
seconds and less).  Result is that timestamps which
include 1000ths of seconds cannot be queried from
Python using mxDateTime values.

PyPgSQL should likely be using code something like the
following to format an mxDateTime value for a timestamp:

new.Format( '%Y-%m-%d %H:%M:%%s' )%( new.second, )

or

new.Format( '%Y-%m-%d %H:%M:%%r' )%( new.second, )

(difference being use of 'r' format, which will do as
much as possible to be sure that the resulting string
is capable of exactly producing the original format).

To illustrate:

from pytable import dbspecifier, sqlquery
spec = dbspecifier.DBSpecifier(
	dbdriver='PyPgSQL',
	database='cinemon',
	host='localhost',
	user='cinemon',
	password='xxxx'
)
driver, connection = spec.connect()
((new,),) = sqlquery.SQLQuery(
	sql = """SELECT MAX( archive_ts ) from log_modem;"""
)( connection )
print 'new', repr(new)
print 'seconds', new.second
records = sqlquery.SQLQuery(
	sql = """SELECT * from log_modem where archive_ts =
%%(new)s;"""
)( connection, new=new ).fetchall()
print records # is an empty list because of truncation...

V:\cinemon>err_date_truncation.py
new <DateTime object for '2003-09-04 19:50:16.30' at
93a820>
seconds 16.297984
[]

----------------------------------------------------------------------

Comment By: Gerhard Häring (ghaering)
Date: 2006-06-22 11:40

Message:
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user_id=163326

Thanks. I'll try to integrate your proposal for 2.5.2.

Sigh. Better late than never.

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