How to access and query objects passed as parameter to a procedure while converting from Oracle to postgresql - oracle

Question

I have a procedure in Oracle that I need to convert to Postgresql and need help on it. It paases a collection of objects in a procedure.The procedure then checks if each object is present in a database table or not and if present it gives a message that , that specific element is found/present. if some element that is paassed to the procedure is not present in the table, the procedure just doesnt do anything. I have to write equivalent of that in postgresql. I think the heart of the issue is this statement:
SELECT COUNT (*)
INTO v_cnt
FROM **TABLE (p_cust_tab_type_i)** pt
WHERE pt.ssn = cc.ssn;
In Oracle a collection can be treated as a table and one can query it but I dont know how to do that in postgresql. The code to create the table, add data, create the procedure, call the procedure by passing the collection (3 objects) and output of that is posted below. Can someone suggest how this can be done in postgresql?
Following the oracle related code and details:
--create table
create table temp_n_tab1
(ssn number,
fname varchar2(20),
lname varchar2(20),
items varchar2(100));
/
--add data
insert into temp_n_tab1 values (1,'f1','l1','i1');
--SKIP no. ssn no. 2 intentionally..
insert into temp_n_tab1 values (3,'f3','l3','i3');
insert into temp_n_tab1 values (4,'f4','l4','i4');
insert into temp_n_tab1 values (5,'f5','l5','i5');
insert into temp_n_tab1 values (6,'f6','l6','i6');
commit;
--create procedure
SET SERVEROUTPUT ON
CREATE OR REPLACE PROCEDURE temp_n_proc (
p_cust_tab_type_i IN temp_n_customer_tab_type)
IS
t_cust_tab_type_i temp_n_customer_tab_type;
v_cnt NUMBER;
v_ssn temp_n_tab1.ssn%TYPE;
CURSOR c
IS
SELECT ssn
FROM temp_n_tab1
ORDER BY 1;
BEGIN
--t_cust_tab_type_i := p_cust_tab_type_i();
FOR cc IN c
LOOP
SELECT COUNT (*)
INTO v_cnt
FROM TABLE (p_cust_tab_type_i) pt
WHERE pt.ssn = cc.ssn;
IF (v_cnt > 0)
THEN
DBMS_OUTPUT.put_line (
'The array element '
|| TO_CHAR (cc.ssn)
|| ' exists in the table.');
END IF;
END LOOP;
EXCEPTION
WHEN OTHERS
THEN
DBMS_OUTPUT.PUT_LINE (SQLERRM);
END;
/
--caller proc
SET SERVEROUTPUT ON
declare
array temp_n_customer_tab_type := temp_n_customer_tab_type();
begin
for i in 1 .. 3
loop
array.extend;
array(i) := temp_n_cust_header_type( i, 'name ' || i, 'lname ' || i,i*i*i*i );
end loop;
temp_n_proc( array );
end;
/
caller proc output:
The array element 1 exists in the table.
The array element 3 exists in the table.

Answer 1

When you create a table in Postgres, a type with the same name is also created. So you can simply pass an array of the table's type as a parameter to the function.
Inside the function you can then use unnest() to treat the array like a table.
The following is the closest match to your original Oracle code:
create function temp_n_proc(p_cust_tab_type_i temp_n_tab1[])
returns void
as
$$
declare
l_rec record;
l_msg text;
l_count integer;
BEGIN
for l_rec in select t1.ssn
from temp_n_tab1 t1
loop
select count(*)
into l_count
from unnest(p_cust_tab_type_i) as t
where t.ssn = l_rec.ssn;
if l_count > 0 then
raise notice 'The array element % exist in the table', l_rec.ssn;
end if;
end loop;
END;
$$
language plpgsql;
The row-by-row processing is not a good idea to begin with (neither in Postgres, nor in Oracle). It would be a lot more efficient to get the existing elements in a single query:
create function temp_n_proc(p_cust_tab_type_i temp_n_tab1[])
returns void
as
$$
declare
l_rec record;
l_msg text;
BEGIN
for l_rec in select t1.ssn
from temp_n_tab1 t1
where t1.ssn in (select t.ssn
from unnest(p_cust_tab_type_i) as t)
loop
raise notice 'The array element % exist in the table', l_rec.ssn;
end loop;
return;
END;
$$
language plpgsql;
You can call the function like this:
select temp_n_proc(array[row(1,'f1','l1','i1'),
row(2,'f2','l2','i2'),
row(3,'f3','l3','i3')
]::temp_n_tab1[]);
However a more "Postgres" like and much more efficient way would be to not use PL/pgSQL for this, but create a simple SQL function that returns the messages as a result:
create or replace function temp_n_proc(p_cust_tab_type_i temp_n_tab1[])
returns table(message text)
as
$$
select format('The array element %s exist in the table', t1.ssn)
from temp_n_tab1 t1
where t1.ssn in (select t.ssn
from unnest(p_cust_tab_type_i) as t)
$$
language sql;
This returns the output of the function as a result rather than using the clumsy raise notice.
You can use it like this:
select *
from temp_n_proc(array[row(1,'f1','l1','i1'),
row(2,'f2','l2','i2'),
row(3,'f3','l3','i3')
]::temp_n_tab1[]);