BUG #7808: unnest doesn't handle nulls in array of composite types correctly

The following bug has been logged on the website:

Bug reference:      7808
Logged by:          Joe Van Dyk
Email address:      joe@tanga.com
PostgreSQL version: 9.2.1
Operating system:   OSX
Description:        =


RhodiumToad says this is a bug in unnest, but honestly I don't quite
understand it all. =


He said: "if you have an array of composite, then a null element provokes
that error, as opposed to an element all of whose columns are null.
basically, unnest(array[null::g])  breaks, while
unnest(array[row(null,null)::g])  works"

My goal is to remove nulls from an array. The array could be an array of a
composite type.

begin;                                                                      =

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create table f (id integer);                                                =

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insert into f values (1), (2);                                              =

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create table g (id integer, f_id integer);                                  =

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insert into g values (1, 1);                                                =

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insert into g values (2, 1);                                                =

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                                                                            =

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create function no_nulls(anyarray) returns anyarray as $$                   =

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  select array(select x from unnest($1) x where not (x is null))            =

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$$ language sql;                                                            =

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select f.id, no_nulls(array_agg(g))                                         =

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from f                                                                      =

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left join g on g.f_id =3D f.id                                             =
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group by f;

                                                                            =

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Expected Result:                                                            =

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 id |     array_agg                                                         =

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----+-------------------                                                    =

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  1 | {"(1,1)","(2,1)"}                                                     =

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  2 | {}                                                                    =

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                                                                            =

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Getting this error:                                                         =

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psql:/tmp/n.sql:18: ERROR:  function returning set of rows cannot return
null value                 =

CONTEXT:  SQL function "no_nulls" statement 1                               =

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 =