MySQL & Perl DBI
In the first chapter of the MySQL Perl tutorial, we will introduce the Perl DBI module and the MySQL database. We will provide some definitions and show how to install the necessary elements.
To work with this tutorial, we must have Perl language, MySQL database,
Perl DBI and
DBD::MySQL modules installed. The DBI is the
standard Perl database interface. Each database has its driver. In our
DBD::mysql is the driver for the MySQL database.
$ sudo perl -MCPAN -e shell cpan> install DBI cpan> install DBD::mysql
The above commands show, how to install Perl DBI and
MySQL is a leading open source database management system. It is a multi user, multithreaded database management system. MySQL is especially popular on the web. It is one part of the very popular LAMP platform consisting of Linux, Apache, MySQL, and PHP. Currently MySQL is owned by Oracle. MySQL database is available on most important OS platforms. It runs on BSD Unix, Linux, Window,s or Mac OS. Wikipedia and YouTube use MySQL. These sites manage millions of queries each day. MySQL comes in two versions: MySQL server system and MySQL embedded system.
The MySQL comes with the
mysql command line utility. It can be used to
issue SQL commands against a database. Now we are going to use the
command line tool to create a new database.
$ sudo apt-get install mysql-server
This command installs the MySQL server and various other packages. While installing the package, we are prompted to enter a password for the MySQL root account. For installing MySQL from sources, have a look at MySQL installation page.
$ service mysql status mysql start/running, process 1238
We check if the MySQL server is running. If not, we need to start the server.
$ sudo service mysql start
The above command is a common way to start MySQL if we have installed the MySQL database from packages.
$ sudo -b /usr/local/mysql/bin/mysqld_safe
The above command starts MySQL server using the MySQL server startup script. The way how we start a MySQL server might be different. It depends whether we have installed MySQL from sources or from packages and also on the Linux distro. For further information consult MySQL first steps or your Linux distro information.
Next, we are going to create a new database user and a new database.
We use the
$ mysql -u root -p Enter password: Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 30 Server version: 5.0.67-0ubuntu6 (Ubuntu) Type 'help;' or '\h' for help. Type '\c' to clear the buffer. mysql> SHOW DATABASES; +--------------------+ | Database | +--------------------+ | information_schema | | mysql | +--------------------+ 2 rows in set (0.00 sec)
We use the mysql monitor client application to connect to the
server. We connect to the database using the root account. We show all
available databases with the
SHOW DATABASES statement.
mysql> CREATE DATABASE mydb; Query OK, 1 row affected (0.02 sec)
We create a new
mydb database. We will use this database throughout
mysql> CREATE USER user12@localhost IDENTIFIED BY '34klq*'; Query OK, 0 rows affected (0.00 sec) mysql> USE mydb; Database changed mysql> GRANT ALL ON mydb.* to user12@localhost; Query OK, 0 rows affected (0.00 sec) mysql> quit; Bye
We create a new database user. We grant all privileges to this user
for all tables of the
The Perl DBI (Database Interface) is a database access module for the Perl programming language. It defines a set of methods, variables and conventions that provide a standard database interface. The DBI is also responsible for the dynamic loading of drivers, error checking and handling, providing default implementations for methods, and many other non-database specific duties. The DBI dispatches method calls to the appropriate database driver. The DBD (Database Driver) is a Perl module which translates the DBI methods for a specific database engine. The database drivers are supplied by database vendors.
#!/usr/bin/perl use strict; use DBI; my @ary = DBI->available_drivers(); print join("\n", @ary), "\n";
The code example lists all available drivers on our system.
We import the DBI module for our script.
my @ary = DBI->available_drivers();
available_drivers() class method gets all the
current available drivers on our system.
print join("\n", @ary), "\n";
This line prints the drivers to the console, each on a separate line.
$ ./available_drivers.pl DBM ExampleP File Gofer Proxy SQLite Sponge mysql
Common DBI methods
The following table lists some common DBI methods.
|Returns a list of all available drivers|
|Establishes a connection to the requested data source|
|Disconnects from the database server|
|Prepares an SQL statement for execution|
|Executes the prepared statement|
|Prepares and executes an SQL statement|
|Associates a value with a placeholder in a prepared statement|
|Binds a Perl variable to an output field of a SELECT statement|
|Starts a new transaction|
|Writes the most recent series of uncommitted database changes to the database|
|Undoes the most recent series of uncommitted database changes|
|Quotes a string literal for use as a literal value in an SQL statement|
|Fetches all the rows and prints them|
|Fetches the next row as an array of fields|
|Fetches the next row as a reference array of fields|
|Fetches the next row as a reference to a hashtable|
|Fetches all data as an array of arrays|
|Finishes a statement and lets the system free resources|
|Returns the number of rows affected|
|Provides information about columns|
|Provides information about tables|
|Provides information about primary keys in tables|
|Provides information about foreign keys in tables|
Perl programmers usually use the following variable names when working with Perl DBI. In this tutorial we will adhere to these conventions too.
|Database handle object|
|Statement handle object|
|Driver handle object (rarely seen or used in applications)|
|Any of the handle types above ($dbh, $sth, or $drh)|
|General Return Code (boolean: true=ok, false=error)|
|General Return Value (typically an integer)|
|List of values returned from the database, typically a row of data|
|Number of rows processed (if available, else -1)|
|NULL values are represented by undefined values in Perl|
|Reference to a hash of attribute values passed to methods|
This chapter of the MySQL Perl tutorial was an introduction to the Perl DBI module and the MySQL database.