PHP Multiple Checkboxes array MySQL

im trying to develop something but my head is a little bit messy

I have two tables in my mysql one is genre which has some values for example: Action, Comedy, Horror the other one is movies, I want for example in the table movies to have results from genre with implode function in php for example: ACTION|COMEDY|HORROR then i want those results to be edited just like in Wordpress where you have the categories and u can change them, i dont know what im doing wrong im using isarray, its displaying but only the results that i have imploded and i want the other results from GENRE table to be displayed as unchecked box