[MySQL learning notes 28] storage function

Stored functions are very similar to stored procedures , See ：【mysql Learning notes 27】 stored procedure
The storage function has a return value , And the parameter can only be in type
grammar ：

CREATE FUNCTION  Function name ([ parameter list ])
RETURNS type [characteristic...]
BEGIN
	--- SQL sentence 
	RETURN ...;
END;

characteristic（ characteristic ）：

• DETERMINISTIC: The same input parameters always produce the same results
• NO SQL: It doesn't contain SQL sentence
• READS SQL DATA: Contains query statements but no write statements

Example

---  Return from 1 To n The cumulative value of 
create function sum(n int)
returns int deterministic
begin
	declare total int default 0;
	while n>0 do
		set total:=total+n;
		set n:=n-1;
	end while;
	return total;
end;