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My SQL Interview Questions and Answers


Adding New User Privileges to MySQL
ou can add users two different ways: by using GRANT statements or by manipulating the MySQL grant tables directly. The preferred method is to use GRANT statements, because they are more concise and less error-prone.

The examples below show how to use the mysql client to set up new users. These examples assume that privileges are set up according to the defaults described in the previous section. This means that to make changes, you must be on the same machine where mysqld is running, you must connect as the MySQL root user, and the root user must have the insert privilege for the mysql database and the reload administrative privilege. Also, if you have changed the root user password, you must specify it for the mysql commands below.

You can add new users by issuing GRANT statements:

shell> mysql --user=root mysql
mysqlgt; GRANT ALL PRIVILEGES ON *.* TO monty@localhost
IDENTIFIED BY 'some_pass' WITH GRANT OPTION;
mysqlgt; GRANT ALL PRIVILEGES ON *.* TO monty@"%"
IDENTIFIED BY 'some_pass' WITH GRANT OPTION;
mysqlgt; GRANT RELOAD,PROCESS ON *.* TO admin@localhost;
mysqlgt; GRANT USAGE ON *.* TO dummy@localhost;

These GRANT statements set up three new users:

monty
A full superuser who can connect to the server from anywhere, but who must use a password 'some_pass' to do so. Note that we must issue GRANT statements for both monty@localhost and monty@"%". If we don't add the entry with localhost, the anonymous user entry for localhost that is created by mysql_install_db will take precedence when we connect from the local host, because it has a more specific Host field value and thus comes earlier in the user table sort order.
admin
A user who can connect from localhost without a password and who is granted the reload and process administrative privileges. This allows the user to execute the mysqladmin reload, mysqladmin refresh, and mysqladmin flush-* commands, as well as mysqladmin process list . No database-related privileges are granted. (They can be granted later by issuing additional GRANT statements.)
dummy
A user who can connect without a password, but only from the local host. The global privileges are all set to 'N' -- the USAGE privilege type allows you to create a user with no privileges. It is assumed that you will grant database-specific privileges later.
You can also add the same user access information directly by issuing INSERT statements and then telling the server to reload the grant tables:

shellgt; mysql --user=root mysql
mysqlgt; INSERT INTO user VALUES('localhost','monty',PASSWORD('some_pass'),
'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y')
mysqlgt; INSERT INTO user VALUES('%','monty',PASSWORD('some_pass'),
'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y')
mysqlgt; INSERT INTO user SET Host='localhost',User='admin',
Reload_priv='Y', Process_priv='Y';
mysqlgt; INSERT INTO user (Host,User,Password)
VALUES('localhost','dummy','');
mysqlgt; FLUSH PRIVILEGES;

Depending on your MySQL version, you may have to use a different number of 'Y' values above (versions prior to Version 3.22.11 had fewer privilege columns). For the admin user, the more readable extended INSERT syntax that is available starting with Version 3.22.11 is used.

Note that to set up a superuser, you need only create a user table entry with the privilege fields set to 'Y'. No db or host table entries are necessary.

The privilege columns in the user table were not set explicitly in the last INSERT statement (for the dummy user), so those columns are assigned the default value of 'N'. This is the same thing that GRANT USAGE does.

The following example adds a user custom who can connect from hosts localhost, server.domain, and whitehouse.gov. He wants to access the bankaccount database only from localhost, the expenses database only from whitehouse.gov, and the customer database from all three hosts. He wants to use the password stupid from all three hosts.

To set up this user's privileges using GRANT statements, run these commands:

shellgt; mysql --user=root mysql
mysqlgt; GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
ON bankaccount.*
TO custom@localhost
IDENTIFIED BY 'stupid';
mysqlgt; GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
ON expenses.*
TO custom@whitehouse.gov
IDENTIFIED BY 'stupid';
mysqlgt; GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
ON customer.*
TO custom@'%'
IDENTIFIED BY 'stupid';

To set up the user's privileges by modifying the grant tables directly, run these commands (note the FLUSH PRIVILEGES at the end):

shellgt; mysql --user=root mysql
mysqlgt; INSERT INTO user (Host,User,Password)
VALUES('localhost','custom',PASSWORD('stupid'));
mysqlgt; INSERT INTO user (Host,User,Password)
VALUES('server.domain','custom',PASSWORD('stupid'));
mysqlgt; INSERT INTO user (Host,User,Password)
VALUES('whitehouse.gov','custom',PASSWORD('stupid'));
mysqlgt; INSERT INTO db
(Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,
Create_priv,Drop_priv)
VALUES
('localhost','bankaccount','custom','Y','Y','Y','Y','Y','Y');
mysqlgt; INSERT INTO db
(Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,
Create_priv,Drop_priv)
VALUES
('whitehouse.gov','expenses','custom','Y','Y','Y','Y','Y','Y');
mysqlgt; INSERT INTO db
(Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,
Create_priv,Drop_priv)
VALUES('%','customer','custom','Y','Y','Y','Y','Y','Y');
mysqlgt; FLUSH PRIVILEGES;

The first three INSERT statements add user table entries that allow user custom to connect from the various hosts with the given password, but grant no permissions to him (all privileges are set to the default value of 'N'). The next three INSERT statements add db table entries that grant privileges to custom for the bankaccount, expenses, and customer databases, but only when accessed from the proper hosts. As usual, when the grant tables are modified directly, the server must be told to reload them (with FLUSH PRIVILEGES) so that the privilege changes take effect.

If you want to give a specific user access from any machine in a given domain, you can issue a GRANT statement like the following:

mysql> GRANT ...
ON *.*
TO myusername@"%.mydomainname.com"
IDENTIFIED BY 'mypassword';

To do the same thing by modifying the grant tables directly, do this:

mysqlgt; INSERT INTO user VALUES ('%.mydomainname.com', 'myusername',
PASSWORD('mypassword'),...);
mysqlgt; FLUSH PRIVILEGES;

You can also use xmysqladmin, mysql_webadmin, and even xmysql to insert, change, and update values in the grant tables. You can find these utilities in the Contrib directory of the MySQL Website.

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