The primary function of the MySQL privilege system is to authenticate a user who connects from a given host and
to associate that user with privileges on a database such as
DELETE. Additional functionality includes the ability to have anonymous users
and to grant privileges for MySQL-specific functions such as
LOAD DATA INFILE and administrative operations.
There are some things that you cannot do with the MySQL privilege system:
You cannot explicitly specify that a given user should be denied access. That is, you cannot explicitly match a user and then refuse the connection.
You cannot specify that a user has privileges to create or drop tables in a database but not to create or drop the database itself.
A password applies globally to an account. You cannot associate a password with a specific object such as a database, table, or routine.
Internally, the server stores privilege information in the grant tables of the
mysql database (that is, in the database named
The MySQL server reads the contents of these tables into memory when it starts and bases access-control
decisions on the in-memory copies of the grant tables.
The MySQL privilege system ensures that all users may perform only the operations permitted to them. As a user, when you connect to a MySQL server, your identity is determined by the host from which you connect and the user name you specify. When you issue requests after connecting, the system grants privileges according to your identity and what you want to do.
MySQL considers both your host name and user name in identifying you because there is no reason to assume that a
given user name belongs to the same person on all hosts. For example, the user
who connects from
office.example.com need not be the same person as the user
joe who connects from
handles this by enabling you to distinguish users on different hosts that happen to have the same name: You can
grant one set of privileges for connections by
and a different set of privileges for connections by
home.example.com. To see what privileges a given account has, use the
SHOW GRANTS statement. For example:
SHOW GRANTS FOR 'joe'@'office.example.com';SHOW GRANTS FOR 'joe'@'home.example.com';
MySQL access control involves two stages when you run a client program that connects to the server:
Stage 1: The server accepts or rejects the connection based on your identity and whether you can verify your identity by supplying the correct password.
Stage 2: Assuming that you can connect, the server checks each
statement you issue to determine whether you have sufficient privileges to perform it. For example, if you try
to select rows from a table in a database or drop a table from the database, the server verifies that you have
SELECT privilege for the
table or the
DROP privilege for
For a more detailed description of what happens during each stage, see Section 6.2.4, "Access Control, Stage 1: Connection Verification", and Section 6.2.5, "Access Control, Stage 2: Request Verification".
If your privileges are changed (either by yourself or someone else) while you are connected, those changes do not necessarily take effect immediately for the next statement that you issue. For details about the conditions under which the server reloads the grant tables, see Section 6.2.6, "When Privilege Changes Take Effect".