I have a Problem with my SQL Syntax, I need your help.

Question

I'm having problems with my SQL Syntax, particularly on Stored Functions/ Stored Procedures. Because instead of the Syntax:
DELIMITER $

CREATE FUNCTION function_name(
param1,
param2,…
)
RETURNS datatype
[NOT] DETERMINISTIC
BEGIN
-- statements
END $

DELIMITER ;
It outputs a syntax error. But when I change it into:

CREATE FUNCTION function_name(
param1,
param2,…
)
RETURNS datatype
DETERMINISTIC
-- statements
It works. But only that It shows a syntax error when I try to turn deterministic into non deterministic, and also when I do other things like declaring a variable, it also shows an error. What I can only do is make a computation by the following syntax:
return(formula);
The same issue for a stored Procedure I tried different ways to fix this. I tried changing the // into ; , tried removing the delimiter, etc but did not work. My theory is that I messed up during the installation process or something, but it's obviously not.
Ps. Already studied SQL, just not in sololearn

Answer 1

I just get a thought that maybe we don't need to wrap the NOT in square brackets as you wrote [NOT] in first sample.

I assume the [] around the NOT were a syntax emphasization to inform that the NOT is an optional statement.