MySQL trigger and values not supplied in update query

Question

there is a way in mysql / mariadb triggers to know if a value is present (set) in the update query?

For example:

    create table MyTest (
    col1 varchar(45),
    col2 varchar(45)
);

insert into MyTest values ( 'val1','val2');

So when I execute

update MyTest set col1 = 'val1.1'

in the trigger I would like to know that col2 is not set.

Thank You

UPDATE (I changed also table schema for better explain my problem)

I have setup a trigger like this

CREATE DEFINER=`root`@`localhost` TRIGGER `MyTest_BEFORE_UPDATE` BEFORE UPDATE ON `MyTest` FOR EACH ROW
BEGIN
    IF (NEW.col2 <=> OLD.col2) THEN
        SET NEW.col2 = 'triggered';
    END IF;
END

If I call

UPDATE MyTest set col1 = 'val1.3'

table will be (this is ok)

+------+---------+
|col1  | col2    |
+------+---------+
|val1.3|triggered|
+------+---------+

but if i call

UPDATE MyTest SET col1='val1.4',col2='val2.4'

first time table is ok

+------+---------+
|col1  | col2    |
+------+---------+
|val1.4|val2.4   |
+------+---------+

but a second update like this

UPDATE MyTest SET col1='val1.5',col2='2.4'

table will be:

+------+---------+
|col1  | col2    |
+------+---------+
|val1.5|triggered|
+------+---------+

instead i would like it should be

+------+---------+
|col1  | col2    |
+------+---------+
|val1.5|val2.4   |
+------+---------+

There is some way i can check this?

Thanks

Answer 1

The Boolean expression

NEW.col2 <=> OLD.col2

can be used in an IF statement (or elsewhere). Notes:

• It tests for whether col2 is changing, it does not test whether you specified col2 without changing it.
• NULL is properly handled because of the <=> operator.

UPDATE (based on further details) See if this comes closer:

IF ( NEW.col1 <=> OLD.col1  -- testing only col1 for changes
 AND NEW.col2 IS NULL)      -- avoiding clobbering col2
    NEW.col2 = 'triggered';

(You haven't yet specified enough use cases to provide a complete solution, but maybe I have given you enough building blocks?)