Can I GRANT ALL PRIVILEGES ON a*.* TO \'my_user\'@\'%\' WITH GRANT OPTION; ?
I just want the user to only have access to all databases beginning with \"
Yes, you can.
This is what phpMyAdmin does when I make a user jaap and use the option Grant all privileges on wildcard name (username\_%):
GRANT ALL PRIVILEGES ON `jaap\_%` . * TO 'jaap'@'localhost';
That's what you mean, right?
PS
As you can see, the _ is escaped, because in (My)SQL an unescaped _ means 'one character'. (Like . in regex.) In this case, you want the _ to be literal, so databases must start with jaap_