6.2.2. Privilege System Grant Tables

Normally, you manipulate the contents of the grant tables in the mysql database indirectly by using statements such as GRANT and REVOKE to set up accounts and control the privileges available to each one. See Section 13.7.1, "Account Management Statements". The discussion here describes the underlying structure of the grant tables and how the server uses their contents when interacting with clients.

These mysql database tables contain grant information:

user: Contains user accounts, global privileges, and other non-privilege columns.
db: Contains database-level privileges.
host: Obsolete. New MySQL installations no longer create this table as of MySQL 5.6.7.
tables_priv: Contains table-level privileges.
columns_priv: Contains column-level privileges.
procs_priv: Contains stored procedure and function privileges.
proxies_priv: Contains proxy-user privileges.

Other tables in the mysql database do not hold grant information and are discussed elsewhere:

event: Contains information about Event Scheduler events: See Section 19.4, "Using the Event Scheduler".
func: Contains information about user-defined functions: See Section 23.3, "Adding New Functions to MySQL".
help_xxx: These tables are used for server-side help: See Section 5.1.10, "Server-Side Help".
plugin: Contains information about server plugins: See Section 5.1.8.1, "Installing and Uninstalling Plugins", and Section 23.2, "The MySQL Plugin API".
proc: Contains information about stored procedures and functions: See Section 19.2, "Using Stored Routines (Procedures and Functions)".
servers: Used by the FEDERATED storage engine: See Section 14.9.2.2, "Creating a FEDERATED Table Using CREATE SERVER".
time_zone_xxx: These tables contain time zone information: See Section 10.6, "MySQL Server Time Zone Support".
Tables with _log in their name are used for logging: See Section 5.2, "MySQL Server Logs".

Each grant table contains scope columns and privilege columns:

Scope columns determine the scope of each row (entry) in the tables; that is, the context in which the row applies. For example, a user table row with Host and User values of 'thomas.loc.gov' and 'bob' would be used for authenticating connections made to the server from the host thomas.loc.gov by a client that specifies a user name of bob. Similarly, a db table row with Host, User, and Db column values of 'thomas.loc.gov', 'bob' and 'reports' would be used when bob connects from the host thomas.loc.gov to access the reports database. The tables_priv and columns_priv tables contain scope columns indicating tables or table/column combinations to which each row applies. The procs_priv scope columns indicate the stored routine to which each row applies.
Privilege columns indicate which privileges are granted by a table row; that is, what operations can be performed. The server combines the information in the various grant tables to form a complete description of a user's privileges. Section 6.2.5, "Access Control, Stage 2: Request Verification", describes the rules that are used to do this.

The server uses the grant tables in the following manner:

The user table scope columns determine whether to reject or permit incoming connections. For permitted connections, any privileges granted in the user table indicate the user's global privileges. Any privilege granted in this table applies to all databases on the server.

Note

Because any global privilege is considered a privilege for all databases, any global privilege enables a user to see all database names with SHOW DATABASES or by examining the SCHEMATA table of INFORMATION_SCHEMA.
The db table scope columns determine which users can access which databases from which hosts. The privilege columns determine which operations are permitted. A privilege granted at the database level applies to the database and to all objects in the database, such as tables and stored programs.
The tables_priv and columns_priv tables are similar to the db table, but are more fine-grained: They apply at the table and column levels rather than at the database level. A privilege granted at the table level applies to the table and to all its columns. A privilege granted at the column level applies only to a specific column.
The procs_priv table applies to stored routines. A privilege granted at the routine level applies only to a single routine.
The proxies_priv table indicates which users can act as proxies for other users and whether proxy users can grant the PROXY privilege to other users.

The server uses the user and db tables in the mysql database at both the first and second stages of access control (see Section 6.2, "The MySQL Access Privilege System"). The columns in the user and db tables are shown here.

Table 6.3. user and db Table Columns

Table Name	`user`	`db`
Scope columns	`Host`	`Host`
	`User`	`Db`
	`Password`	`User`
Privilege columns	`Select_priv`	`Select_priv`
	`Insert_priv`	`Insert_priv`
	`Update_priv`	`Update_priv`
	`Delete_priv`	`Delete_priv`
	`Index_priv`	`Index_priv`
	`Alter_priv`	`Alter_priv`
	`Create_priv`	`Create_priv`
	`Drop_priv`	`Drop_priv`
	`Grant_priv`	`Grant_priv`
	`Create_view_priv`	`Create_view_priv`
	`Show_view_priv`	`Show_view_priv`
	`Create_routine_priv`	`Create_routine_priv`
	`Alter_routine_priv`	`Alter_routine_priv`
	`Execute_priv`	`Execute_priv`
	`Trigger_priv`	`Trigger_priv`
	`Event_priv`	`Event_priv`
	`Create_tmp_table_priv`	`Create_tmp_table_priv`
	`Lock_tables_priv`	`Lock_tables_priv`
	`References_priv`	`References_priv`
	`Reload_priv`
	`Shutdown_priv`
	`Process_priv`
	`File_priv`
	`Show_db_priv`
	`Super_priv`
	`Repl_slave_priv`
	`Repl_client_priv`
	`Create_user_priv`
	`Create_tablespace_priv`
Security columns	`ssl_type`
	`ssl_cipher`
	`x509_issuer`
	`x509_subject`
	`plugin`
	`authentication_string`
	`password_expired`
Resource control columns	`max_questions`
	`max_updates`
	`max_connections`
	`max_user_connections`

The mysql.user table plugin and authentication_string columns store authentication plugin information.

If the plugin column for an account row is empty, the server uses native authentication for connection attempts for the account: Clients must match the password in the Password column of the account row.

If an account row names a plugin in the plugin column, the server uses it to authenticate connection attempts for the account. Whether the plugin uses the value in the Password column is up to the plugin.

The password_expired column was added in MySQL 5.6.6 to permit DBAs to expire account passwords and require users to reset their password. The default password_expired value is 'N', but can be set to 'Y' with the ALTER USER statement. After an account's password has been expired, all operations performed by the account in subsequent connections to the server result in an error until the user issues a SET PASSWORD statement to establish a new account password. See Section 13.7.1.1, "ALTER USER Syntax".

It is possible after password expiration to "reset" a password by using SET PASSWORD to set it to its current value. As a matter of good policy, it is preferable to choose a different password.

Caution

In MySQL 5.6.6, ALTER USER also sets the Password column to the empty string, so do not use this statement until 5.6.7.

During the second stage of access control, the server performs request verification to make sure that each client has sufficient privileges for each request that it issues. In addition to the user and db grant tables, the server may also consult the tables_priv and columns_priv tables for requests that involve tables. The latter tables provide finer privilege control at the table and column levels. They have the columns shown in the following table.

Table 6.4. tables_priv and columns_priv TableColumns

Table Name	`tables_priv`	`columns_priv`
Scope columns	`Host`	`Host`
	`Db`	`Db`
	`User`	`User`
	`Table_name`	`Table_name`
		`Column_name`
Privilege columns	`Table_priv`	`Column_priv`
	`Column_priv`
Other columns	`Timestamp`	`Timestamp`
	`Grantor`

The Timestamp and Grantor columns are set to the current timestamp and the CURRENT_USER value, respectively. However, they are unused and are discussed no further here.

For verification of requests that involve stored routines, the server may consult the procs_priv table, which has the columns shown in the following table.

Table 6.5. procs_priv Table Columns

Table Name	`procs_priv`
Scope columns	`Host`
	`Db`
	`User`
	`Routine_name`
	`Routine_type`
Privilege columns	`Proc_priv`
Other columns	`Timestamp`
	`Grantor`

The Routine_type column is an ENUM column with values of 'FUNCTION' or 'PROCEDURE' to indicate the type of routine the row refers to. This column enables privileges to be granted separately for a function and a procedure with the same name.

The Timestamp and Grantor columns currently are unused and are discussed no further here.

The proxies_priv table records information about proxy users. It has these columns:

Host, User: These columns indicate the user account that has the PROXY privilege for the proxied account.
Proxied_host, Proxied_user: These columns indicate the account of the proxied user.
Grantor: Currently unused.
Timestamp: Currently unused.
With_grant: This column indicates whether the proxy account can grant the PROXY privilege to other accounts.

Scope columns in the grant tables contain strings. They are declared as shown here; the default value for each is the empty string.

Table 6.6. Grant Table Scope Column Types

Column Name	Type
`Host`, `Proxied_host`	`CHAR(60)`
`User`, `Proxied_user`	`CHAR(16)`
`Password`	`CHAR(41)`
`Db`	`CHAR(64)`
`Table_name`	`CHAR(64)`
`Column_name`	`CHAR(64)`
`Routine_name`	`CHAR(64)`

For access-checking purposes, comparisons of User, Proxied_user, Password, Db, and Table_name values are case sensitive. Comparisons of Host, Proxied_host, Column_name, and Routine_name values are not case sensitive.

In the user and db tables, each privilege is listed in a separate column that is declared as ENUM('N','Y') DEFAULT 'N'. In other words, each privilege can be disabled or enabled, with the default being disabled.

In the tables_priv, columns_priv, and procs_priv tables, the privilege columns are declared as SET columns. Values in these columns can contain any combination of the privileges controlled by the table. Only those privileges listed in the column value are enabled.

Table 6.7. Set-Type Privilege Column Values

Table Name	Column Name	Possible Set Elements
`tables_priv`	`Table_priv`	`'Select', 'Insert', 'Update', 'Delete', 'Create', 'Drop', 'Grant', 'References', 'Index', 'Alter', 'Create View','Show view', 'Trigger'`
`tables_priv`	`Column_priv`	`'Select', 'Insert', 'Update', 'References'`
`columns_priv`	`Column_priv`	`'Select', 'Insert', 'Update', 'References'`
`procs_priv`	`Proc_priv`	`'Execute', 'Alter Routine', 'Grant'`

Administrative privileges (such as RELOAD or SHUTDOWN) are specified only in the user table. Administrative operations are operations on the server itself and are not database-specific, so there is no reason to list these privileges in the other grant tables. Consequently, to determine whether you can perform an administrative operation, the server need consult only the user table.

The FILE privilege also is specified only in the user table. It is not an administrative privilege as such, but your ability to read or write files on the server host is independent of the database you are accessing.

The mysqld server reads the contents of the grant tables into memory when it starts. You can tell it to reload the tables by issuing a FLUSH PRIVILEGES statement or executing a mysqladmin flush-privileges or mysqladmin reload command. Changes to the grant tables take effect as indicated in Section 6.2.6, "When Privilege Changes Take Effect".

When you modify an account's privileges, it is a good idea to verify that the changes set up privileges the way you want. To check the privileges for a given account, use the SHOW GRANTS statement (see Section 13.7.5.22, "SHOW GRANTS Syntax"). For example, to determine the privileges that are granted to an account with user name and host name values of bob and pc84.example.com, use this statement:

SHOW GRANTS FOR 'bob'@'pc84.example.com';