Need help on UPDATE query This is my table tracks

id | art | time



id is an auto-increment primary key 
art is a varchar(512) 
time is a timestamp not null predefined as current_timestamp and on update current_timestamp


It seems really a dumb question but after one hour of tries, someone could please tell me why this simple query doesn't UPDATE the rows with empty art field but instead UPDATE only the time to 0000-00-00 00:00:00?

UPDATE `tracks` SET `time` = `time` AND `art` = 'default.jpg' WHERE `art` = '';


UPDATE

I ran SELECT * FROM tracks WHERE art = ''; and it founds right rows, same using WHERE TRIM(art) = '' .
Instead WHERE art IS NULL is empty.

UPDATE2

This query works but it updates the time and I don't want it.

UPDATE `tracks` SET `art` = 'default1.jpg' WHERE `art` = '';
The initial syntax was incorrect

UPDATE `tracks` SET `time` = `time` AND `art` = 'default.jpg' WHERE `art` = '';


AND does not separate the columns to update. They should be separated by commas (,)

What you probably wanted was 

UPDATE `tracks` SET `time` = `time`,`art` = 'default.jpg' WHERE `art` = '';