PostgreSQL equivalent of Oracle "bulk collect" - postgresql

Question

In PostgreSQL exists some ways to make a statement using bulk collect into like in Oracle?
Example in Oracle:
create or replace procedure prc_tst_bulk_test is
type typ_person is table of tb_person%rowtype;
v_tb_person typ_person;
begin
select *
bulk collect into v_tb_person
from tb_person;
-- make a selection in v_tb_person, for instance
select name, count(*) from v_tb_person where age > 50
union
select name, count(*) from v_tb_person where gender = 1
end;

Answer 1

In PostgreSQL 10 you can use array_agg:
declare
v_ids int[];
begin
select array_agg(id) INTO v_ids
from mytable1
where host = p_host;
--use v_ids...
end;
You'll have array and it can be used to make select from it using unnest:
select * from unnest(v_ids) where ...

Answer 2

There is no such syntax in PostgreSQL, nor a close functional equivalent.
You can create a temporary table in your PL/PgSQL code and use that for the desired purpose. Temp tables in PL/PgSQL are a little bit annoying because the names are global within the session, but they work correctly in PostgreSQL 8.4 and up.
A better alternative for when you're doing all the work within a single SQL statement is to use a common table expression (CTE, or WITH query). This won't be suitable for all situations.
The example above would be much better solved by a simple RETURN QUERY in PL/PgSQL, but I presume your real examples are more complex.
Assuming that tb_person is some kind of expensive-to-generate view that you don't just want to scan in each branch of the union, you could do something like:
CREATE OR REPLACE FUNCTION prc_tst_bulk()
RETURNS TABLE (name text, rowcount integer) AS
$$
BEGIN
RETURN QUERY
WITH v_tb_person AS (SELECT * FROM tb_person)
select name, count(*) from v_tb_person where age > 50
union
select name, count(*) from v_tb_person where gender = 1;
END;
$$ LANGUAGE plpgsql;
This particular case can be further simplified into a plain SQL function:
CREATE OR REPLACE FUNCTION prc_tst_bulk()
RETURNS TABLE (name text, rowcount integer) AS
$$
WITH v_tb_person AS (SELECT * FROM tb_person)
select name, count(*) from v_tb_person where age > 50
union
select name, count(*) from v_tb_person where gender = 1;
$$ LANGUAGE sql;

Answer 3

You can use a PostgreSQL arrays too - it is similar to Oracle's collections:
postgres=# create table _foo(a int, b int);
CREATE TABLE
postgres=# insert into _foo values(10,20);
INSERT 0 1
postgres=# create or replace function multiply()
returns setof _foo as $$
/*
* two tricks are here
* table name can be used as type name
* table name can be used as fictive column that packs all fields
*/
declare a _foo[] = (select array(select _foo from _foo));
begin
return query select * from unnest(a)
union
all select * from unnest(a);
end;
$$ language plpgsql;
CREATE FUNCTION
postgres=# select * from multiply();
a | b
----+----
10 | 20
10 | 20
(2 rows)
But in your case Craig Ringer's proposal is perfect and should be preferable.

Answer 4

-- Fetch the next 5 rows in the cursor_01:
FETCH FORWARD 5 FROM cursor_01;
PostgreSQL 10+ works.
https://www.postgresql.org/docs/10/sql-fetch.html