User can't access a database

Question

In my PHP script, I\'m accessing two databases db1 and db2. I have a user myuser@localhost that can access db1 but can\'

Answer 1

According to the mysql manual here:

If you modify the grant tables indirectly using account-management statements such as GRANT, REVOKE, or SET PASSWORD, the server notices these changes and loads the grant tables into memory again immediately.

If you modify the grant tables directly using statements such as INSERT, UPDATE, or DELETE, your changes have no effect on privilege checking until you either restart the server or tell it to reload the tables. If you change the grant tables directly but forget to reload them, your changes have no effect until you restart the server. This may leave you wondering why your changes do not seem to make any difference!

This does seem to be true in most cases. However, in my situation I was working with an Amazon Web Services (AWS) RDS mysql instance. After many unsuccessful attempts to grant the user permissions I tried a FLUSH PRIVILEGES and the database was immediately visible to the user. If you come across this while looking for a solution on the Amazon Web Services RDS platform you might want to give this a try and see if it helps.

This SO question contains the most complete solutions to this problem and is the first in most search results so I wanted to add this response for anyone using RDS. Hopefully it will save RDS admins some time.