Create function or stored proc with interval variable - sql

Question

I am new to PostgreSQL but have been working with MSSQL for years. I am currently working with PostgreSQL 13.
In MSSQL I have a script that creates an offset for dates so that I can create a fiscal calendar in the same date table as my regular calendar. I just add the offset to the date in the row and it adjusts my fiscal year as needed.
I am trying to preform something like this in PostgreSQL. I have some code working to do what I want. However, now I am trying to write a function or stored procedure to automate this code. I am having issues converting the code to work in a function or stored procedure.
My code I have working looks like this. This is a very trimmed down version of the code for illustration purposes.
DO $$
DECLARE daydiff INTERVAL;
DECLARE startdate DATE;
DECLARE enddate DATE;
DECLARE fiscalstartdate DATE;
BEGIN
-- Populate these variables
startdate:=(date '2017-01-01');
enddate:=(date '2017-12-31');
fiscalstartdate:=(date '2016-09-01');
-- Calculate date diff
daydiff:=make_interval(days => startdate - fiscalstartdate);
-- Insert records into table
INSERT INTO master.Calendar (
full_date
, year
, fiscal_year
)
SELECT
CAST(generate_series AS date) AS full_date
, EXTRACT(YEAR FROM generate_series)::INTEGER AS year
, EXTRACT(YEAR FROM generate_series + daydiff)::INTEGER AS fiscal_year
FROM (
SELECT generate_series(
startdate::timestamp,
enddate::timestamp,
interval '1 days'
)
) a;
END $$;
It does exactly what I want to do. However, I want to be able to call that in a function or stored procedure to automate rebuilding of tables and data. I then tried a few different things, but where I am at right now is this. Again, this is the trimmed down version, but still the issue is present.
CREATE OR REPLACE PROCEDURE create_calendar_table(startdate DATE, enddate DATE, fiscalstartdate DATE) AS $$
DECLARE
daydiff INTERVAL;
BEGIN
-- Calculate date diff
daydiff:=make_interval(days => startdate - fiscalstartdate);
-- Insert records into table
INSERT INTO master.Calendar (
full_date
, year
, fiscal_year
)
SELECT
CAST(generate_series AS date) AS full_date
, EXTRACT(YEAR FROM generate_series)::INTEGER AS year
, EXTRACT(YEAR FROM generate_series + daydiff)::INTEGER AS fiscal_year
FROM (
SELECT generate_series(
startdate::timestamp,
enddate::timestamp,
interval '1 days'
)
) a;
END $$ LANGUAGE SQL;
I receive an error of 'syntax error at or near "INTERVAL"'. I have tried a few things like trying to add a DO $$ in there and that did not seem to work well at all. Very well could be my ignorance on this version of SQL. The best I can tell is that I can't declare an INTERVAL type when creating a procedure or function like I can in the DO $$.
How can I get around this or what is the proper way of doing this in PostgreSQL? Any help is greatly appreciated.

Answer 1

You need language plpgsql - you can't use variables inside a SQL function.