PHP and MySQL Web Development - P44 pptx

182 Chapter 8 Creating Your Web Database n Setting up your path n Running mysql_install_db, if required n Setting the root password n Deleting the anonymous user and the test database n Starting the MySQL server and setting it up to run automatically If you’ve done all those things, you can go right ahead and read this chapter. If you haven’t, you can find instructions on how to do these things in Appendix A, “Installing PHP 4 and MySQL.” If you have problems at any point in this chapter, it might be because your MySQL system is not set up correctly. If that happens, refer back to this list and Appendix A to make sure that your setup is correct. n Have access to MySQL on a machine that you do not administer such as a Web hosting service, a machine at your workplace, and so on. If this is the case, in order to work through the examples or to create your own database, you’ll need to have your administrator set up a user and database for you to work with and tell you the username, password, and database name they have assigned to you. You can either skip the sections of this chapter that explain how to set up users and databases or read them in order to better explain what you need to your system administrator. As a normal user, you won’t be able to execute the commands to create users and databases. The examples in this chapter were all built and tested with MySQL version 3.23.52. Some earlier versions of MySQL have less functionality.You should install or upgrade to the most current stable release at the time of reading.You can download the current release from the MySQL site at http://mysql.com. A Note on Using the MySQL Monitor You will notice that the MySQL examples in this chapter and the next end each command with a semicolon (;).This tells MySQL to execute the command. If you leave off the semicolon, nothing will happen.This is a common problem for new users. This also means that you can have new lines in the middle of a command.We have used this to make the examples easier to read.You will see where we have done this because MySQL provides a continuation symbol. It’s an arrow that looks like this: mysql> grant select -> 11 525x ch08 1/24/03 3:39 PM Page 182 183 How to Log in to MySQL This means MySQL is expecting more input. Until you type the semicolon, you will get these characters each time you press Enter. Another point to note is that SQL statements are not case sensitive, but database and table names can be—more on this later. How to Log in to MySQL To do this, go to a command line interface on your machine and type the following: mysql -h hostname -u username -p Your command prompt might look different depending on the operating system and shell you are using. The mysql command invokes the MySQL monitor.This is a command line client that connects you to the MySQL server. The -h switch is used to specify the host to which you want to connect; that is, the machine on which the MySQL server is running. If you’re running this command on the same machine as the MySQL server, you can leave out this switch and the hostname parameter. If not, you should replace the hostname parameter with the name of the machine where the MySQL server is running. The -u switch is used to specify the username you want to connect as. If you do not specify, the default will be the username you are logged into the operating system as. If you have installed MySQL on your own machine or server, you will need to log in as root and create the database we’ll use in this section.Assuming that you have a clean install, root is the only user you’ll have to begin with. If you are using MySQL on a machine administered by somebody else, use the username they gave you. The -p switch tells the server you want to connect using a password.You can leave it out if a password has not been set for the user you are logging in as. If you are logging in as root and have not set a password for root,I strongly recommend that you visit Appendix A and do so right now.Without a root password, your system is insecure. You don’t need to include the password on this line.The MySQL server will ask you for it. In fact, it’s better if you don’t. If you enter the password on the command line, it will appear as plain text on the screen, and will be quite simple for other users to discover. After you have entered the previous command, you should get a response something like this: Enter password: **** (If this hasn’t worked, verify that the MySQL server is running, and the mysql command is somewhere in your path.) Yo u should enter your password. If all goes well, you should see a response something like this: 11 525x ch08 1/24/03 3:39 PM Page 183 184 Chapter 8 Creating Your Web Database Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 5 to server version: 3.23.52-nt Type 'help;' or '\h' for help. Type '\c' to clear the buffer. mysql> On your own machine: If you don’t get a response similar to this, make sure that you have run mysql_install_db if required, you have set the root password, and you’ve typed it in correctly. If it isn’t your machine, make sure that you typed in the password correctly. You should now be at a MySQL command prompt, ready to create the database. If you are using your own machine, follow the guidelines in the next section. If you are using somebody else’s machine, this should already have been done for you. You can jump ahead to the “Using the Right Database” section.You might want to read the intervening sections for general background, but you won’t be able to run the commands specified there. (Or at least you shouldn’t be able to!) Creating Databases and Users The MySQL database system can support many different databases.You will generally have one database per application. In our Book-o-Rama example, the database will be called books. Creating the Database This is the easiest part. At the MySQL command prompt, type mysql> create database dbname; You should substitute the name of the database you want to create for dbname.To begin creating the Book-O-Rama example, you can create a database called books. That’s it.You should see a response like Query OK, 1 row affected (0.06 sec) This means everything has worked. If you don’t get this response, make sure that you typed the semicolon at the end of the line. A semicolon tells MySQL that you are fin- ished, and it should actually execute the command. Users and Privileges A MySQL system can have many users.The root user should generally be used for administration purposes only, for security reasons. For each user who needs to use the system, you will need to set up an account and password.These do not need to be the same as usernames and passwords outside of MySQL (for example, UNIX or NT usernames and passwords).The same principle applies to root. It is a good idea to have different passwords for the system and for MySQL, especially when it comes to the root password. 11 525x ch08 1/24/03 3:39 PM Page 184 185 Introduction to MySQL’s Privilege System It isn’t compulsory to set up passwords for users, but we strongly recommend that you set up passwords for all the users that you create. For the purposes of setting up a Web database, it’s a good idea to set up at least one user per Web application. You might ask, “Why would I want to do this?”—the answer lies in privileges. Introduction to MySQL’s Privilege System One of the best features of MySQL is that it supports a sophisticated privilege system. A privilege is the right to perform a particular action on a particular object, and is associated with a particular user.The concept is very similar to file permissions. When you create a user within MySQL, you grant her a set of privileges to specify what she can and cannot do within the system. Principle of Least Privilege The principle of least privilege can be used to improve the security of any computer system. It’s a basic, but very important principle that is often overlooked.The principle is as follows: A user (or process) should have the lowest level of privilege required in order to perform his assigned task. It applies in MySQL as it does elsewhere. For example, to run queries from the Web, a user does not need all the privileges to which root has access.We should therefore create another user who only has the necessary privileges to access the database we have just created. Setting Up Users: The GRANT Command The GRANT and REVOKE commands are used to give and take away rights to and from MySQL users at four levels of privilege.These levels are n Global n Database n Tabl e n Column We’ll see in a moment how each of these can be applied. The GRANT command is used to create users and give them privileges.The general form of the GRANT command is GRANT privileges [columns] ON item TO user_name [IDENTIFIED BY 'password'] [WITH GRANT OPTION] 11 525x ch08 1/24/03 3:39 PM Page 185 186 Chapter 8 Creating Your Web Database The clauses in square brackets are optional.There are a number of placeholders in this syntax. The first, privileges, should be a comma separated list of privileges. MySQL has a defined set of these.They are described in the next section. The columns placeholder is optional.You can use it to specify privileges on a column-by-column basis.You can use a single column name or a comma-separated list of column names. The item placeholder is the database or table to which the new privileges apply. You can grant privileges on all the databases by specifying *.* as the item.This is called granting global privileges.You can also do this by specifying * alone if you are not using any particular database. More commonly, you will specify all tables in a database as dbname.*, on a single table as dbname.tablename, or on specific columns by specifying dbname. tablename and some specific columns in the columns placeholder.These represent the three other levels of privilege available: database, table,and column,respectively. If you are using a specific database when you issue this command, tablename on its own will be interpreted as a table in the current database. The user_name should be the name you want the user to log in as in MySQL. Remember that it does not have to be the same as a system login name.The user_name in MySQL can also contain a hostname.You can use this to differentiate between, say, laura (interpreted as laura@localhost) and laura@somewhere.com.This is quite useful because users from different domains often have the same name. It also increases security because you can specify where users can connect from, and even which tables or databases they can access from a particular location. The password should be the password you want the user to log in with.The usual rules for selecting passwords apply.We will talk more about security later, but a password should not be easily guessable.This means that a password should not be a dictionary word or the same as the username. Ideally, it will contain a mixture of upper- and lower- case and nonalphabetic characters. The WITH GRANT OPTION option, if specified, allows the specified user to grant her own privileges to others. Privileges are stored in four system tables, in the database called mysql.These four tables are called mysql.user, mysql.db, mysql.tables_priv, and mysql.columns_priv, and relate directly to the four levels of privilege mentioned earlier. As an alternative to GRANT,you can alter these tables directly.We will discuss this in more detail in Chapter 11,“Advanced MySQL.” Types and Levels of Privilege Three basic types of privileges exist in MySQL: privileges suitable for granting to regular users, privileges suitable for administrators, and a couple of special privileges.Any user can be granted any of these privileges, but it’s usually sensible to restrict the administrator type ones to administrators, according to the principle of least privilege. 11 525x ch08 1/24/03 3:39 PM Page 186 . the MySQL site at http:/ /mysql. com. A Note on Using the MySQL Monitor You will notice that the MySQL examples in this chapter and the next end each command with a semicolon (;).This tells MySQL. database and table names can be—more on this later. How to Log in to MySQL To do this, go to a command line interface on your machine and type the following: mysql -h hostname -u username -p Your. command prompt might look different depending on the operating system and shell you are using. The mysql command invokes the MySQL monitor.This is a command line client that connects you to the MySQL