what is good solution for support NULL inside string_to_array function?
Hello
I understand why we don't support expression 'null'::sometype. But it
does problems with array deserialisation.
postgres=# select array_to_string(ARRAY[10,20,30,NULL,30], '|');
array_to_string
-----------------
10|20|30|30
(1 row)
quietly removing NULL is maybe good for compatibility but is wrong for
functionality. Can we enhance function array_to_string and
string_to_array like:
CREATE OR REPLACE FUNCTION array_to_string(dta anyarray, sep text,
nullsym text)
RETURNS text AS $$
SELECT array_to_string(ARRAY(SELECT coalesce(v::text,$3)
FROM unnest($1) g(v)),$2)
$$ LANGUAGE sql;
CREATE FUNCTION
Time: 231.445 ms
postgres=# select array_to_string(ARRAY[10,20,30,NULL,30], '|', '');
array_to_string
-----------------
10|20|30||30
(1 row)
Time: 230.879 ms
postgres=# select array_to_string(ARRAY[10,20,30,NULL,30], '|', 'NULL');
array_to_string
------------------
10|20|30|NULL|30
(1 row)
Time: 2.031 ms
CREATE OR REPLACE FUNCTION string_to_array(str text, sep text, nullsym text)
RETURNS text[] AS $$
SELECT ARRAY(SELECT CASE WHEN v <> $3 THEN v ELSE NULL END
FROM unnest(string_to_array($1,$2)) g(v))
$$ LANGUAGE sql;
CREATE FUNCTION
Time: 29.044 ms
postgres=# SELECT string_to_array('10,20,30,,40',',','');
string_to_array
--------------------
{10,20,30,NULL,40}
(1 row)
postgres=# SELECT string_to_array('10,20,30,,40',',','')::int[];
string_to_array
--------------------
{10,20,30,NULL,40}
(1 row)
it is correct?
other ideas?
Regards
Pavel Stehule
quietly removing NULL is maybe good for compatibility but is wrong for
functionality.
I agree. I wasn't aware of this little misfeature.
Default display for NULL should be a zero-length string.
--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com
Josh Berkus <josh@agliodbs.com> writes:
quietly removing NULL is maybe good for compatibility but is wrong for
functionality.
I agree. I wasn't aware of this little misfeature.
Default display for NULL should be a zero-length string.
That's just as broken as Pavel's suggestion. Unless you have something
that is guaranteed distingishable from the output of any non-null value,
you really can't make a significant improvement here.
regards, tom lane
Tom Lane wrote:
Default display for NULL should be a zero-length string.
That's just as broken as Pavel's suggestion. Unless you have something
that is guaranteed distingishable from the output of any non-null value,
you really can't make a significant improvement here.
Right. This is the problem we solved in CSV processing by distinguishing
between quoted and unquoted values that could be null - the CSV rule is
that a null value isn't quoted.
cheers
andrew
2010/5/4 Tom Lane <tgl@sss.pgh.pa.us>:
Josh Berkus <josh@agliodbs.com> writes:
quietly removing NULL is maybe good for compatibility but is wrong for
functionality.I agree. I wasn't aware of this little misfeature.
Default display for NULL should be a zero-length string.
That's just as broken as Pavel's suggestion. Unless you have something
that is guaranteed distingishable from the output of any non-null value,
you really can't make a significant improvement here.
I wouldn't modify current two params string_to_array and
array_to_string function. So there are not any default string (maybe
empty string) for NULL. My proposal is new three params functions with
explicit<<< "null string" definition. This cannot break
compatibility and enhance functionality - It is just short cut for
code from my proposal - in C this functionality can by implemented
much faster.
Regards
Pavel
Show quoted text
regards, tom lane
2010/5/4 Josh Berkus <josh@agliodbs.com>:
quietly removing NULL is maybe good for compatibility but is wrong for
functionality.I agree. I wasn't aware of this little misfeature.
Default display for NULL should be a zero-length string.
I disagree - NULL is NULL, not empty string (Oracle is different)
if array_to_string is equivalent to
x[1] || sep || x[2] || sep || x[3] || sep ....
then correct result is NULL
and then string_to_array and array_to_string are correct, because
string_to_array cannot contain any NULL symbol.
Regards
Pavel Stehule
Show quoted text
--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com
2010/5/4 Pavel Stehule <pavel.stehule@gmail.com>:
2010/5/4 Tom Lane <tgl@sss.pgh.pa.us>:
Josh Berkus <josh@agliodbs.com> writes:
quietly removing NULL is maybe good for compatibility but is wrong for
functionality.I agree. I wasn't aware of this little misfeature.
Default display for NULL should be a zero-length string.
That's just as broken as Pavel's suggestion. Unless you have something
that is guaranteed distingishable from the output of any non-null value,
you really can't make a significant improvement here.I wouldn't modify current two params string_to_array and
array_to_string function. So there are not any default string (maybe
empty string) for NULL. My proposal is new three params functions withexplicit<<< "null string" definition. This cannot break
compatibility and enhance functionality - It is just short cut for
code from my proposal - in C this functionality can by implemented
much faster.
I did some coding - the patch can be very simple
postgres=# select array_to_string(array[1,2,3,4,5,null],',','*');
array_to_string
-----------------
1,2,3,4,5,*
(1 row)
Time: 0,501 ms
postgres=# select
string_to_array(array_to_string(array[1,2,3,4,5,null],',','*'),',','*');
string_to_array
------------------
{1,2,3,4,5,NULL}
(1 row)
Time: 0,617 ms
postgres=# select string_to_array('1,2,3,4,5,*',',','*')::int[];
string_to_array
------------------
{1,2,3,4,5,NULL}
(1 row)
Time: 0,652 ms
and then string_to_array and array_to_string are orthogonal with NULL.
Pavel
Show quoted text
Regards
Pavelregards, tom lane
Attachments:
3params_arrayfce.diffapplication/octet-stream; name=3params_arrayfce.diffDownload+69-11
On Tue, May 4, 2010 at 10:05 AM, Pavel Stehule <pavel.stehule@gmail.com> wrote:
and then string_to_array and array_to_string are orthogonal with NULL.
I like the behavior, but should it share the name with the 2 argument
version given the incompatibility? Maybe make a new function
to_string(anyarray, sep, nullsym='') and deprecate the old one?
merlin
2010/5/4 Merlin Moncure <mmoncure@gmail.com>:
On Tue, May 4, 2010 at 10:05 AM, Pavel Stehule <pavel.stehule@gmail.com> wrote:
and then string_to_array and array_to_string are orthogonal with NULL.
I like the behavior, but should it share the name with the 2 argument
version given the incompatibility? Maybe make a new function
to_string(anyarray, sep, nullsym='') and deprecate the old one?
maybe to_string X to_array ... Why not? It shorter, maybe it is cleaner
Regards
Pavel
Show quoted text
merlin
Tom Lane wrote:
Josh Berkus <josh@agliodbs.com> writes:
quietly removing NULL is maybe good for compatibility but is wrong for
functionality.I agree. I wasn't aware of this little misfeature.
Default display for NULL should be a zero-length string.
That's just as broken as Pavel's suggestion. Unless you have something
that is guaranteed distingishable from the output of any non-null value,
you really can't make a significant improvement here.regards, tom lane
Is this, perhaps, a generalized case of this long-running discussion
from last year?:
http://archives.postgresql.org/pgsql-hackers/2009-03/msg01350.php
Cheers,
Steve