pgsql concat for number returning null - postgresql

Question

I have created a sequence like below:
CREATE SEQUENCE public.shiwangini_seq
INCREMENT BY 1
MINVALUE 1
MAXVALUE 9223372036854775807
START 150037
CACHE 1
NO CYCLE;
After this - I have created a function which will use this sequence to generate next value:
create or replace function shiwangini_unq(out v_final_value2 bigint) as $$
declare
v_seq_value bigint;
v_shard_id bigint;
v_final_value2 bigint ;
begin
select nextval('shiwangini_seq') into v_seq_value ;
v_shard_id := 2;
select concat (v_seq_value , v_shard_id ) into v_final_value2 ;
end ;
$$ language plpgsql ;
Now, this function returns null whenever I call it. Like below:
select shiwangini_unq(); ----null
I checked concat() manages type conversion itself. Even after that, in my case it's returning null. I help will be really appreciated to make it working. Thanks in advance!

Answer 1

You can write this as normal SQL function (without OUT parameter) and eliminate all data conversations.
create or replace
function shiwangini_unq()
returns bigint
language sql
as $$
select 10*nextval('shiwangini_seq')+2;
$$;
OR just get rid of the function altogether.
create sequence shiwangini_seqX start with 12 increment by 10;
See demo

Answer 2

Your main problem is, that the variable v_final_value2 overshadows your out parameter.
But all that isn't needed to begin with.
You should declare a proper return type. But you are overcomplicating things here. You can make this more efficient without PL/pgSQL and a simple SQL function:
create or replace function shiwangini_unq()
return bigint
as $$
select concat(nextval('shiwangini_seq'), 2)::bigint;
$$ language sql;

Answer 3

You give the return type of your function as an input, that is the problem. The below code is working well for me if there any error please text me back.
Try this
create or replace function shiwangini_unq() returns bigint as $$
declare
v_seq_value bigint;
v_shard_id bigint;
v_final_value2 bigint ;
begin
select nextval('shiwangini_seq') into v_seq_value ;
v_shard_id := 2;
select concat (v_seq_value, v_shard_id ) into v_final_value2 ;
return v_final_value2;
end ;
$$ language plpgsql ;