More than three exclusion clauses not firing trigger in MySQL - mysql

Question

I am writing a query to track changes in a few tables based on a trigger as we have users that access the database directly and through the front-end. I have written out a trigger that verifies that columns we do not care about do not get touched, but when I add more than three to the if not statement the trigger suddenly stops firing. Is this a limitation in MySQL or am I doing something wrong? Thanks!
Here is the ChangesTracker Table schema:
CREATE TABLE `Test_Automation`.`ChangesTracker` (
`tracking_id` INT NOT NULL AUTO_INCREMENT,
`table_name` VARCHAR(45) NOT NULL,
`timestamp` DATETIME NULL DEFAULT CURRENT_TIMESTAMP,
`Operation` VARCHAR(45) NOT NULL,
`tracking_query` VARCHAR(1024) NOT NULL COMMENT '\'\'',
`tracking_user_id` VARCHAR(45) NOT NULL,
`uuid` VARCHAR(45) NOT NULL,
PRIMARY KEY (`tracking_id`))
COMMENT = 'Table for tracking SQL update and delete statements executed into the database to monitor changes.';
Then the trigger itself:
/*********************/
DROP TRIGGER IF EXISTS sample_table_log_update;
DELIMITER |
CREATE TRIGGER sample_table_log_update
BEFORE UPDATE ON `sample_table`
FOR EACH ROW
IF NOT ((NEW.excluded <> OLD.excluded) OR (NEW.reserved <> OLD.reserved) OR (NEW.healthy <> OLD.healthy) OR (NEW.router <> OLD.router)) THEN
BEGIN
DECLARE original_query VARCHAR(1024);
SET original_query = (SELECT info FROM INFORMATION_SCHEMA.PROCESSLIST WHERE id = CONNECTION_ID());
INSERT INTO `ChangesTracker`(`table_name`, `timestamp`, `operation`, `tracking_query`, `tracking_user_id`, `uuid`) VALUES ('sample_table', CURRENT_TIMESTAMP, 'Update', original_query, CURRENT_USER, old.uuid);
END;
END IF
;
|

Answer 1

Studies have shown that in 98.67% +/- 7.29% of cases this is caused by a null value:
You cannot use arithmetic comparison operators such as =, <, or <> to test for NULL. [...] Because the result of any arithmetic comparison with NULL is also NULL, you cannot obtain any meaningful results from such comparisons.
Comparing null to anything with <> will return null, and IF NOT (null) is never fulfilled. Since the 4th comparison causes you trouble, I assume that either NEW.router or OLD.router are null.
You can use e.g. the NULL-safe equal to operator <=>:
NULL-safe equal. This operator performs an equality comparison like the = operator, but returns 1 rather than NULL if both operands are NULL, and 0 rather than NULL if one operand is NULL.
Please note that <=> checks for equality (even if it might look similar to <>), so e.g. (NEW.excluded <> OLD.excluded) would translate to !(NEW.excluded <=> OLD.excluded).