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Sort order confusion

P: n/a
I am suffering some sort order confusion. Given a database, "foo",
with a single character(4) column of data left padded with spaces I
get:

select * from foo order by somechars;

somechars
-----------
0
1
10
100
1011
111
1512
2
222
3
333

The output I desire is a basic ASCII sort:

somechars
-----------
0
1
2
3
10
100
111
222
333
1011
1512

(This sample set just has spaces and numeric digits but could have
other characters - I want the output in ASCII sort order)

1. What is the correct way to do this?

2. How do I verify the locale setting of an existing database cluster
(to verify that I really initialized it as "initdb -d --locale=C -D
/var/lib/pgsql/data")?

3. Should I have included "--enable-locale" or similar option when I
built Postgresql (the build is vanilla 7.4.1 "./configure ; make ;
make install")?

Cheers,
Steve
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Nov 22 '05 #1
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7 Replies


P: n/a
On Fri, 2004-02-06 at 11:12, Steve Crawford wrote:
I am suffering some sort order confusion. Given a database, "foo",
with a single character(4) column of data left padded with spaces I
get:

select * from foo order by somechars;

somechars
-----------
0
1
10
100
1011
111
1512
2
222
3
333

The output I desire is a basic ASCII sort:

somechars
-----------
0
1
2
3
10
100
111
222
333
1011
1512

(This sample set just has spaces and numeric digits but could have
other characters - I want the output in ASCII sort order)


Your original sort is a basic lexigraphic ("alphabetical" by ASCII
character set number) sort.

What you appear to want is a numeric sort, where the numbers come out in
the order of numbers, rather than in their ASCII character set order.

If there were just digits that would be fairly easy, but I can't see any
way (short of post-processing the list in other software or writing
yourself a stored procedure) to do it in SQL.

Stephen

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Nov 22 '05 #2

P: n/a
On Thursday 05 February 2004 4:21 pm, Stephen Robert Norris wrote:
On Fri, 2004-02-06 at 11:12, Steve Crawford wrote:
I am suffering some sort order confusion. Given a database,
"foo", with a single character(4) column of data left padded with
spaces I get:

select * from foo order by somechars;

somechars
-----------
0
1
10
100
1011
111
1512
2
222
3
333
<snip>

Your original sort is a basic lexigraphic ("alphabetical" by ASCII
character set number) sort.

What you appear to want is a numeric sort, where the numbers come
out in the order of numbers, rather than in their ASCII character
set order.


Not exactly. I _DO_ want it in ASCII character set order which
includes spaces (0x20) sorting ahead of digits (0x30 - 0x39). This is
not what is happening. The first sort is some SQL sort order that
seems to ignore certain characters. Note the different sort order if
I pad with 'x' instead of '<space>':

somechars
-----------
1011
1512
x100
x111
x222
x333
x444
x555
x666
x777
x888
xx10
xx44
xx55
xxx0
xxx1
xxx2
xxx3
xxx4
xxx5
xxx6
xxx7
xxx8
xxx9
xxxx

Naturally if I were dealing with fields guaranteed to have something
that would convert to an int I could just order by, say,
int4(somechars) but that is not the case.

I even tried the to_ascii function but apparently that's the wrong
approach:
ERROR: encoding conversion from SQL_ASCII to ASCII not supported

Cheers,
Steve
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Nov 22 '05 #3

P: n/a
On Fri, Feb 06, 2004 at 11:21:41AM +1100, Stephen Robert Norris wrote:
On Fri, 2004-02-06 at 11:12, Steve Crawford wrote:
I am suffering some sort order confusion. Given a database, "foo",
with a single character(4) column of data left padded with spaces I
get:

select * from foo order by somechars;


Cast it:

alvherre=> select * from foo order by bar::text::int;
bar
------
0
1
10
33
100
101
333
503
(8 filas)

--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
"La naturaleza, tan frágil, tan expuesta a la muerte... y tan viva"

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Nov 22 '05 #4

P: n/a
On Thursday 05 February 2004 5:01 pm, Alvaro Herrera wrote:
On Fri, Feb 06, 2004 at 11:21:41AM +1100, Stephen Robert Norris

wrote:
On Fri, 2004-02-06 at 11:12, Steve Crawford wrote:
I am suffering some sort order confusion. Given a database,
"foo", with a single character(4) column of data left padded
with spaces I get:

select * from foo order by somechars;


Cast it:

alvherre=> select * from foo order by bar::text::int;
bar
------
0
1
10
33
100
101
333
503
(8 filas)


Can't. As noted in the original post the column may contain data that
won't convert to an int (all spaces, characters, punctuation). I'm
seeking generic true ASCII sort order.

Cheers,
Steve
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Nov 22 '05 #5

P: n/a
On Thu, 5 Feb 2004, Steve Crawford wrote:
2. How do I verify the locale setting of an existing database cluster
(to verify that I really initialized it as "initdb -d --locale=C -D
/var/lib/pgsql/data")?


I think it'd be
pg_controldata /var/lib/pgsql/data
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Nov 22 '05 #6

P: n/a
Steve Crawford <sc*******@pinpointresearch.com> writes:
Not exactly. I _DO_ want it in ASCII character set order which
includes spaces (0x20) sorting ahead of digits (0x30 - 0x39). This is
not what is happening. The first sort is some SQL sort order that
seems to ignore certain characters.


Sounds to me like you've got the database in a non-C locale. See past
discussions ...

regards, tom lane

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Nov 22 '05 #7

P: n/a
On Thursday 05 February 2004 6:08 pm, Tom Lane wrote:
Steve Crawford <sc*******@pinpointresearch.com> writes:
Not exactly. I _DO_ want it in ASCII character set order which
includes spaces (0x20) sorting ahead of digits (0x30 - 0x39).
This is not what is happening. The first sort is some SQL sort
order that seems to ignore certain characters.


Sounds to me like you've got the database in a non-C locale. See
past discussions ...


That was my first inclination (as noted in the full version of my
original post - now lost to the thread) but my installation history
showed:
initdb -d --locale=C -D /var/lib/pgsql/data

Nonetheless pg_controldata shows:
LC_COLLATE: en_US
LC_CTYPE: en_US

I now suspect that currently active "real" database was in-fact
created not by my several test initializations but by the SuSE
startup script which will run an "initdb" if the database has not
been initialized and which reads /etc/sysconfig/language to get
default locale settings.

So...

Is there a method of changing the locale of an extant database or do I
need to dump ; delete db ; reinit ; restore ?

Cheers,
Steve
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Nov 22 '05 #8

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