Re: BUG #7730: intarray representation of empty arrays

Thanks for looking into this. Finally I'll get to test  existing columns fil=
led with a variety of array[0], '{}' and array[0]-array[0] or Null. Sorry it=
 took so long.=20

What is the target production release?

A. Elein Mustain
Elein@varlena.com
510-637-9106

> On Sep 7, 2013, at 8:44 AM, Bruce Momjian <bruce@momjian.us> wrote:
>=20
>=20
> Applied.
>=20
> --------------------------------------------------------------------------=
-
>=20
>> On Wed, Sep  4, 2013 at 03:01:50PM -0400, Bruce Momjian wrote:
>>> On Wed, Dec  5, 2012 at 12:44:39AM +0000, elein@varlena.com wrote:
>>> The following bug has been logged on the website:
>>>=20
>>> Bug reference:      7730
>>> Logged by:          elein
>>> Email address:      elein@varlena.com
>>> PostgreSQL version: 9.2.1
>>> Operating system:   Linux
>>> Description:       =20
>>>=20
>>> select NULLIF('{1,2,3}'::integer[] - '{3,2,1}'::integer[], '{}'::integer=
[]);
>>> This returns an empty array.  It should return NULL.=20
>>>=20
>>> Per RhodiumToad: the core code represents '{}' as an array with 0
>>> dimensions, whereas intarray represents it as an array with 1 dimension b=
ut
>>> 0 elements
>>>=20
>>> intarray should use the same standards as the core code if possible.  I
>>> peered at the code and don't see anything untoward but did not have time=
 to
>>> spend on it.
>>=20
>> I just got time to look at this, and it is certainly easier to see when
>> you use array_dims():
>>=20
>>    SELECT '{1,2,3}'::integer[] - '{3,2,1}'::integer[];
>>     ?column?
>>    ----------
>>     {}
>>   =20
>>    SELECT array_dims('{1,2,3}'::integer[] - '{3,2,1}'::integer[]);
>>     array_dims
>>    ------------
>>     [1:0]
>>   =20
>>    SELECT array_dims('{}'::integer[]);
>>     array_dims
>>    ------------
>>     (null)
>>=20
>> This is part of the larger TODO item of how to handle empty
>>> =3D1-dimensional empty arrays vs. zero-dimensional empty arrays, which i=
s
>> discussed here:
>>=20
>>    https://wiki.postgresql.org/wiki/Todo#Arrays
>>    Improve handling of empty arrays
>>=20
>> In that thread, no one could find a way to create a 1-dimensional empty
>> array at the SQL level, but thanks to intarray, you found a way.  It is
>> natural that intarray, being mostly used for one-dimensional arrays,
>> would return a 1-dimensional empty array.  However, besides being
>> inconsistent, as you mentioned, there is also no way to dump/restore
>> one-dimensional empty arrays, which is a larger concern.
>>=20
>> I have developed the attached patch to force empty intarray results to
>> be zero-dimensional empty arrays, rather than 1-dimensional empty
>> arrays.  With this patch, a zero-dimensional empty array is returned:
>>=20
>>    SELECT array_dims('{1,2,3}'::integer[] - '{3,2,1}'::integer[]);
>>     array_dims
>>    ------------
>>     (null)
>>=20
>> --=20
>>  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
>>  EnterpriseDB                             http://enterprisedb.com
>>=20
>>  + It's impossible for everything to be true. +
>=20
>> diff --git a/contrib/intarray/_int_tool.c b/contrib/intarray/_int_tool.c
>> new file mode 100644
>> index 8635576..fc462b2
>> *** a/contrib/intarray/_int_tool.c
>> --- b/contrib/intarray/_int_tool.c
>> *************** resize_intArrayType(ArrayType *a, int nu
>> *** 246,251 ****
>> --- 246,258 ----
>>      int            nbytes =3D ARR_DATA_OFFSET(a) + sizeof(int) * num;
>>      int            i;
>>=20
>> +    /* if no elements, return a zero-dimensional array */
>> +    if (num =3D=3D 0)
>> +    {
>> +        ARR_NDIM(a) =3D 0;
>> +        return a;
>> +    }
>> +=20
>>      if (num =3D=3D ARRNELEMS(a))
>>          return a;
>=20
>>=20
>> --=20
>> Sent via pgsql-bugs mailing list (pgsql-bugs@postgresql.org)
>> To make changes to your subscription:
>> http://www.postgresql.org/mailpref/pgsql-bugs
>=20
>=20
> --=20
>  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
>  EnterpriseDB                             http://enterprisedb.com
>=20
>  + It's impossible for everything to be true. +
>=20