Error when creating stored procedure in postgres - postgresql

Question

I am trying to convert an oracle stored procedure to Postgres function/procedure.
I did some research and read many forums to prepare the syntax for the stored procedure in postgres.
But getting an error for declaring an integer variable.
My code is like below:
The purpose of my procedure is to load one-month records into another month (EX: load Jan 2020 data into March 2020)
Postgres Procedure:
CREATE OR REPLACE FUNCTION Corporate.copy_forecast(code OUT integer, message OUT VARCHAR)
LANGUAGE plpgsql
AS $$
DECLARE
v_current_month integer;
v_previous_month integer;
begin
select max(cycleid) into v_previous_month, max(cycleid)+1 into v_current_month from Corporate.forecast;
INSERT INTO Corporate.forecast
(SELECT v_current_month,lob,delivery,forecast_val
FROM Corporate.forecast
WHERE month= v_previous_month);
code:=1;
message:='Sucussfully loaded previous month forecast to current month';
exception
when others then
code:=0;
message:='Failed';
END;
$$
Please help me to fix the above procedure.

Answer 1

There are several problems with your code:
The first one is simple: you say LANGUAGE sql, but you write PL/pgSQL code.
That explains the error message you get. Use LANGUAGE plpgsql if you want to write PL/pgSQL.
You are using variables that are the same as column names, which leads to ambiguity. For example, you declare
current_month integer;
previous_month integer;
but you have a WHERE clause
WHERE current_month = previous_month
where obviously one of them should refer to a variable and the other to a table column. That will not work and cause errors.
The best and simplest solution is to always use variable names that are different from column names. A simple method is to start all variable names with v_.
A second option is to always qualify columns with the table name and variables with the function name.

Answer 2

You do not have a problem declaring an integer variable it is much larger you have structural problems. Below I indicate those issues and will then show corrections. The indicator "--<< ..." discusses the line(s) just above it.
CREATE OR REPLACE FUNCTION copy_forecast(code OUT integer, message OUT VARCHAR)
--<< Improper format Should be (out code integer, out message varchar)
--<< and while not invalid IMHO bad design a function/procedure should just do its job correctly or raise an exception
returns ???
--<< This is missing. A Postgres Function MUST declare what it returns, if nothing then RETURNS VOID. But I guess this was an Oracle Procedure.
LANGUAGE plpgsql
AS $$
DECLARE
v_current_month integer;
v_previous_month integer;
begin
select max(cycleid) into v_previous_month, max(cycleid)+1 into v_current_month from forecast;
--<< Invalid format Should Be select var1,var2 into local1, local2 ...
INSERT INTO forecast
--<< Very dangerous. If table ever changes this will fail.
(SELECT v_current_month,lob,delivery,forecast_val
FROM forecast
WHERE month= v_previous_month);
code:=1;
message:='Successfully loaded previous month forecast to current month';
exception
when others then
code:=0;
message:='Failed'
--<< Very dangerous (all 3 lines). When an error occurs you will never know what it is. See insert above
;
END;
$$;
The following corrects the errors indicated above. Again the indicator (--*) discussed the line(s) above it.
create or replace function copy_forecast()
returns boolean
language plpgsql
as $$
declare
v_current_month integer;
v_previous_month integer;
begin
select max(cycleid)
, max(cycleid)+1
into v_previous_month
, v_current_month
from forecast;
insert into forecast (cycleid,lob,delivery,forcast_val )
select v_current_month,lob,delivery,forecast_val
from forecast
where month= v_previous_month);
--* insert will fail I cannot resolve. MONTH not inserted, but must exist on table.
--* It seems you are using cycleid and month as synonyms
return True;
--* you can leave the out parameters if desirded. Set them before the return
exception
when others then
-- Log the error and debug information here
return false;
--* you can leave out parameters if desired Set them before the return.
end;
This should correct the structure issues with your function. However, the logical issue with month/cycleid remains.
However, this does not actually get you to your goal. As stated "the purpose of my procedure is to load one-month records into another month (EX: load Jan 2020 data into March 2020)". This function CANNOT do that. It can only copy the latest month/cycleid to the next month/cycleid; so Jan->Feb, Feb->Mar, ... Nov->Dec. But Dec->Jan would fail unless month/cycleid can be 13, and subsequent months would continue increasing month/cycle. Accomplishing your goal required INPUT parameters for the Source(from) and Target(to). And as #LaurenzAlbe said "no moving targets". That would be another question.