Can someone help me with functions in MySQL? - mysql

Question

I run the following script:
USE MODERN_FAMILY;
DROP FUNCTION IF EXISTS compare_news;
DELIMITER $$
CREATE FUNCTION compare_news(n INT, m INT)
RETURNS VARCHAR(20)
BEGIN
DECLARE s VARCHAR(20);
IF n>m THEN SET s='>';
ELSEIF n=m THEN SET s='=';
ELSE SET s='<';
END IF;
SET s = CONCAT(n, ' ', s, ' ',m);
RETURN s; END;$$
First script returns this error :
Error Code: 1418. This function has none of DETERMINISTIC, NO SQL, or READS SQL DATA in its declaration and binary logging is enabled (you might want to use the less safe log_bin_trust_function_creators variable).
Then, I run this:
USE MODERN_FAMILY;
SELECT compare_news(2,5);
It returns this error:
Error Code: 2014. Commands out of sync; you can't run this command now.
Does someone know if I have an error with the script? Or is related to my SQL configuration?

Answer 1

log_bin_trust_function_creators variable controls whether binary logging should trust the stored function creators for not to create unsafe stored functions.
Reference: Stored Program Logging
When you create a stored function, you must declare either that it is
deterministic or that it does not modify data. Otherwise, it may be
unsafe for data recovery or replication.
By default, for a CREATE FUNCTION statement to be accepted, at least
one of DETERMINISTIC, NO SQL, or READS SQL DATA must be specified
explicitly. Otherwise an error occurs:
ERROR 1418 (HY000): This function has none of DETERMINISTIC, NO SQL,
or READS SQL DATA in its declaration and binary logging is enabled
(you *might* want to use the less safe log_bin_trust_function_creators
variable)
To relax the preceding conditions on function creation (that you must
have the SUPER privilege and that a function must be declared
deterministic or to not modify data), set the global
log_bin_trust_function_creators system variable to 1.
Solution 1: Make your function which doesn't manipulate data or deterministic in nature
CREATE FUNCTION `compare_news`(
`n` INT,
`m` INT
) RETURNS VARCHAR(20) CHARSET latin1 LANGUAGE SQL DETERMINISTIC NO SQL SQL SECURITY DEFINER COMMENT ''
BEGIN
DECLARE s VARCHAR(20);
IF n>m THEN
SET s='>';
ELSEIF n=m THEN
SET s='=';
ELSE
SET s='<';
END IF;
SET s = CONCAT(n, ' ', s, ' ',m);
RETURN s;
END
Solution 2: Enable MySQL to trust such functions by setting mysql log_bin_trust_function_creators variable to ON.
Reference: log_bin_trust_function_creators
SET GLOBAL log_bin_trust_function_creators = 1;
The variable will change upon restart if you do not update the config to reflect the change.