[Pypgsql-devel] [ pypgsql-Bugs-1056030 ] Numeric datatype loses digits

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Bugs item #1056030, was opened at 2004-10-28 07:29
Message generated for change (Settings changed) made by ballie01
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Category: libpq
Group: None
>Status: Pending
>Resolution: Fixed
Priority: 5
Submitted By: Peer (peergriebel)
Assigned to: Nobody/Anonymous (nobody)
Summary: Numeric datatype loses digits

Initial Comment:
  select * from table
results in data rows. If the table includes numeric
columns digits are truncated: 4.56 will be returned as
4.6.  This does not happen using a statement like this:
  select * from table order by somecolumn


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>Comment By: Billy G. Allie (ballie01)
Date: 2005-02-23 00:40

Message:
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Changed code so that if the PgNumeric  prec/scale changes,
then it iwll use the new prec/sacle.  For example:

>>> cur.execute("""
... SELECT 123.4::numeric UNION
... SELECT 12345.4321::numeric UNION
... SELECT 0.00000987654321::numeric""")
>>> cur.fetchone()
[<PgNumeric instance - precision: 15 scale: 14 value:
0.00000987654321>]
>>> cur.fetchone()
[<PgNumeric instance - precision: 4 scale: 1 value: 123.4>]
>>> cur.fetchone()
[<PgNumeric instance - precision: 9 scale: 4 value: 12345.4321>]
>>>

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Comment By: Peer (peergriebel)
Date: 2004-10-28 09:06

Message:
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user_id=1133977

After some investigation I discovered some more facts. You need:

0. (Use PgSQL 1.35)
1. A table with at least one numeric column (no precision,
no scale)
2. Insert data with different precision. E.g 3.1 and 4.56.
3. SELECT all rows from db with different ordering so that
first value (3.1) will be returned first/with second value
(4.56) returned first.

Then PgSQL tries to determine the precision of the numeric
column. Since the databse does not tell it tries to guess
(line #2859). It will guess by first value. So if 3.1 comes
first it guesses precision is 1. BUT THIS IS WRONG. If the
first fetched value is 4.56 it will guess precision is 2. 
Since the TypeCache uses it's knowlegde for all rows the
guessing is sometimes wrong.


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