Overview of MySQL & PHP

What is Database?

A database is a separate application that stores a collection of data. Each database has one or more distinct APIs for creating, accessing, managing, searching and replicating the data it holds.

Other kinds of data stores can be used, such as files on the file system or large hash tables in memory but data fetching and writing would not be so fast and easy with those types of systems.

So nowadays, we use relational database management systems (RDBMS) to store and manage huge volume of data. This is called relational database because all the data is stored into different tables and relations are established using primary keys or other keys known as foreign keys.

A Relational DataBase Management System (RDBMS) is a software that:

1. Enables you to implement a database with tables, columns and indexes.
2. Guarantees the Referential Integrity between rows of various tables.
3. Updates the indexes automatically.
4. Interprets an SQL query and combines information from various tables.

RDBMS 

Before we proceed to explain MySQL database system, let's revise few definitions related to database.

1. Database: A database is a collection of tables, with related data.
2. Table: A table is a matrix with data. A table in a database looks like a simple spreadsheet.
3. Column: One column (data element) contains data of one and the same kind, for example the column postcode.
4. Row: A row (= tuple, entry or record) is a group of related data, for example the data of one subscription.
5. Redundancy: Storing data twice, redundantly to make the system faster.
6. Primary Key: A primary key is unique. A key value can not occur twice in one table. With a key, you can find at most one row.
7. Foreign Key: A foreign key is the linking pin between two tables.
8. Compound Key: A compound key (composite key) is a key that consists of multiple columns, because one column is not sufficiently unique.
9. Index: An index in a database resembles an index at the back of a book.
10. Referential Integrity: Referential Integrity makes sure that a foreign key value always points to an existing row.

MySQL

MySQL is a fast, easy-to-use RDBMS being used for many small and big businesses. MySQL is developed, marketed, and supported by MySQL AB, which is a Swedish company. MySQL is becoming so popular because of many good reasons:

1. MySQL is released under an open-source license. So you have nothing to pay to use it.
2. MySQL is a very powerful program in its own right. It handles a large subset of the functionality of the most expensive and powerful database packages.
3. MySQL uses a standard form of the well-known SQL data language.
4. MySQL works on many operating systems and with many languages including PHP, PERL, C, C++, JAVA, etc.
5. MySQL works very quickly and works well even with large data sets.
6. MySQL is very friendly to PHP, the most appreciated language for web development.
7. MySQL supports large databases, up to 50 million rows or more in a table. The default file size limit for a table is 4GB, but you can increase this (if your operating system can handle it) to a theoretical limit of 8 million terabytes (TB).
8. MySQL is customizable. The open-source GPL license allows programmers to modify the MySQL software to fit their own specific environments.

How To Installing MySQL on Windows:

Default installation on any version of Windows is now much easier than it used to be, as MySQL now comes neatly packaged with an installer. Simply download the installer package, unzip it anywhere, and run setup.exe.

Default installer setup.exe will walk you through the trivial process and by default will install everything under C:\mysql.

Test the server by firing it up from the command prompt the first time. Go to the location of the mysqld server which is probably C:\mysql\bin, and type:

mysqld.exe --console

NOTE: If you are on NT, then you will have to use mysqld-nt.exe instead of mysqld.exe

If all went well, you will see some messages about startup and InnoDB. If not, you may have a permissions issue. Make sure that the directory that holds your data is accessible to whatever user (probably mysql) the database processes run under.

MySQL will not add itself to the start menu, and there is no particularly nice GUI way to stop the server either. Therefore, if you tend to start the server by double clicking the mysqld executable, you should remember to halt the process by hand by using mysqladmin, Task List, Task Manager, or other Windows-specific means.

Verifying MySQL Installation:

After MySQL has been successfully installed, the base tables have been initialized, and the server has been started, you can verify that all is working as it should via some simple tests.

Use the mysqladmin Utility to Obtain Server Status:

Use mysqladmin binary to check server version. This binary would be available in /usr/bin on linux and in C:\mysql\bin on windows.

[root@host]# mysqladmin --version

It will produce the following result on Linux. It may vary depending on your installation:

mysqladmin  Ver 8.23 Distrib 5.0.9-0, for redhat-linux-gnu on i386

If you do not get such message, then there may be some problem in your installation and you would need some help to fix it.

Execute simple SQL commands using MySQL Client:

You can connect to your MySQL server by using MySQL client using mysql command. At this moment, you do not need to give any password as by default it will be set to blank.

So just use following command

[root@host]# mysql

It should be rewarded with a mysql> prompt. Now, you are connected to the MySQL server and you can execute all the SQL command at mysql> prompt as follows:

mysql> SHOW DATABASES;
+----------+
| Database |
+----------+
| mysql    |
| test     |
+----------+
2 rows in set (0.13 sec)

Post-installation Steps:

MySQL ships with a blank password for the root MySQL user. As soon as you have successfully installed the database and client, you need to set a root password as follows:

[root@host]# mysqladmin -u root password "new_password";

Now to make a connection to your MySQL server, you would have to use the following command:

[root@host]# mysql -u root -p
Enter password:*******

UNIX users will also want to put your MySQL directory in your PATH, so you won't have to keep typing out the full path every time you want to use the command-line client. For bash, it would be something like:

export PATH=$PATH:/usr/bin:/usr/sbin

Running MySQL at boot time:

If you want to run MySQL server at boot time, then make sure you have following entry in /etc/rc.local file.

/etc/init.d/mysqld start

Also,you should have mysqld binary in /etc/init.d/ directory.

Running and Shutting down MySQL Server:

First check if your MySQL server is running or not. You can use the following command to check this:

 ps -ef | grep mysqld

If your MySql is running, then you will see mysqld process listed out in your result. If server is not running, then you can start it by using the following command:

root@host# cd /usr/bin
./safe_mysqld &

Now, if you want to shut down an already running MySQL server, then you can do it by using the following command:

root@host# cd /usr/bin
./mysqladmin -u root -p shutdown
Enter password: ******

Setting Up a MySQL User Account:

For adding a new user to MySQL, you just need to add a new entry to user table in database mysql.

Below is an example of adding new user guest with SELECT, INSERT and UPDATE privileges with the password guest123; the SQL query is:

root@host# mysql -u root -p
Enter password:*******
mysql> use mysql;
Database changed

mysql> INSERT INTO user 
          (host, user, password, 
           select_priv, insert_priv, update_priv) 
           VALUES ('localhost', 'guest', 
           PASSWORD('guest123'), 'Y', 'Y', 'Y');
Query OK, 1 row affected (0.20 sec)

mysql> FLUSH PRIVILEGES;
Query OK, 1 row affected (0.01 sec)

mysql> SELECT host, user, password FROM user WHERE user = 'guest';
+-----------+---------+------------------+
| host      | user    | password         |
+-----------+---------+------------------+
| localhost | guest | 6f8c114b58f2ce9e |
+-----------+---------+------------------+
1 row in set (0.00 sec)

When adding a new user, remember to encrypt the new password using PASSWORD() function provided by MySQL. As you can see in the above example the password mypass is encrypted to 6f8c114b58f2ce9e.

Notice the FLUSH PRIVILEGES statement. This tells the server to reload the grant tables. If you don't use it, then you won't be able to connect to mysql using the new user account at least until the server is rebooted.

You can also specify other privileges to a new user by setting the values of following columns in user table to 'Y' when executing the INSERT query or you can update them later using UPDATE query.

1. Select_priv
2. Insert_priv
3. Update_priv
4. Delete_priv
5. Create_priv
6. Drop_priv
7. Reload_priv
8. Shutdown_priv
9. Process_priv
10. File_priv
11. Grant_priv
12. References_priv
13. Index_priv
14. Alter_priv

Another way of adding user account is by using GRANT SQL command; following example will add user zara with password zara123 for a particular database called TUTORIALS.

root@host# mysql -u root -p password;
Enter password:*******
mysql> use mysql;
Database changed

mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
    -> ON TUTORIALS.*
    -> TO 'zara'@'localhost'
    -> IDENTIFIED BY 'zara123';

This will also create an entry in mysql database table called user.

NOTE: MySQL does not terminate a command until you give a semi colon (;) at the end of SQL command.

The /etc/my.cnf File Configuration:

Most of the cases, you should not touch this file. By default, it will have the following entries:

[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock

[mysql.server]
user=mysql
basedir=/var/lib

[safe_mysqld]
err-log=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

Here, you can specify a different directory for error log, otherwise you should not change any entry in this table.

Administrative MySQL Command:

Here is the list of important MySQL commands, which you will use time to time to work with MySQL database:

1. USE Databasename : This will be used to select a particular database in MySQL workarea.
2. SHOW DATABASES: Lists the databases that are accessible by the MySQL DBMS.
3. SHOW TABLES: Shows the tables in the database once a database has been selected with the use command.
4. SHOW COLUMNS FROM tablename: Shows the attributes, types of attributes, key information, whether NULL is permitted, defaults, and other information for a table.
5. SHOW INDEX FROM tablename: Presents the details of all indexes on the table, including the PRIMARY KEY.
6. SHOW TABLE STATUS LIKE tablename\G: Reports details of the MySQL DBMS performance and statistics.