Couldn't cast to record[]

Hi

čt 3. 3. 2022 v 11:01 odesílatel Suresh Kumar R <suresh.arsenal29@gmail.com>
napsal:

Hi, I created an table with composite type array as datatype for one
column.
When I query that table I need the pg_typeof(column) as record[] instead of
composite_type[].
I tried creating a separate function and returning record[], but below
error
is thrown,

ERROR: PL/pgSQL functions cannot return type record[]

Below is sample for my requirement.

pali=# create type address as (number bigint, city varchar);
CREATE TYPE
pali=# create table person(name varchar, addresses address[]);
CREATE TABLE
pali=# insert into person values ('Michael', array[(82, 'NYC'),(24,
'Dunkirk')]::address[]);
INSERT 0 1
pali=# select pg_typeof(addresses::record[]) from person ;
pg_typeof
-----------
address[]

Here I expect record[] instead of address[].

Thanks in advance.

record type is not real PostgreSQL's type. It is just PLpgSQL only type.
You cannot use it outside PLpgSQL.

Regards

Pavel

Suresh Kumar R <suresh.arsenal29@gmail.com> writes:

When I query that table I need the pg_typeof(column) as record[] instead of
composite_type[].

Why? record[] is considered a pseudotype (polymorphic type),
which is why casting to it doesn't do anything.

regards, tom lane

On Thu, Mar 3, 2022 at 4:01 AM Suresh Kumar R
<suresh.arsenal29@gmail.com> wrote:

Hi, I created an table with composite type array as datatype for one column.
When I query that table I need the pg_typeof(column) as record[] instead of
composite_type[].
I tried creating a separate function and returning record[], but below error
is thrown,

ERROR: PL/pgSQL functions cannot return type record[]

Below is sample for my requirement.

pali=# create type address as (number bigint, city varchar);
CREATE TYPE
pali=# create table person(name varchar, addresses address[]);
CREATE TABLE
pali=# insert into person values ('Michael', array[(82, 'NYC'),(24,
'Dunkirk')]::address[]);
INSERT 0 1
pali=# select pg_typeof(addresses::record[]) from person ;
pg_typeof
-----------
address[]

Here I expect record[] instead of address[].

Why do you think you need this? If you need variant record storage,
you probably want to go to jsonb, then use jsonb_populate_recordset to
convert back to specific type.

merlin

Hi Merlin,
I needed this because, I use postgres backend along with golang using
pgx driver. When i query address i need to specify OID of
address[](composite type). In my case i couldnt find the oid of that type
since its dynamic. Needed generic type so needed to cast to record[] which
has constant oid.

With regards
Suresh kumar R

On Fri, 4 Mar, 2022, 11:28 pm Merlin Moncure, <mmoncure@gmail.com> wrote:

Suresh Kumar R <suresh.arsenal29@gmail.com> writes:

I needed this because, I use postgres backend along with golang using
pgx driver. When i query address i need to specify OID of
address[](composite type). In my case i couldnt find the oid of that type
since its dynamic.

The usual advice is to look it up on the fly. As an example:

regression=# create type address as (f1 text, f2 text);
CREATE TYPE
regression=# select 'address[]'::regtype;
regtype
-----------
address[]
(1 row)

regression=# select 'address[]'::regtype::oid;
oid
--------
127056
(1 row)

If the client-side stack wants a type OID for a result column,
it's unlikely to be satisfied with a pseudotype OID anyway.
That provides next-to-no useful information about how to
interpret values. Are you sure you can't just leave the type
unspecified (e.g. zero) in whatever API is giving you trouble?

regards, tom lane