Install MySQL/Ruby using the Ruby Gems packaging manager:
Email:
["m", "o", "c", ".", "l", "i", "a", "m", "g", "2", "+", "T", "F", "I", "H", "S", "o", "u", "l", ".", "m", "o", "t"].reverse.join

1. Get a list all mysql packages installed on your machine.
 sudo dpkg -l |grep mysql

2. sudo apt-get install libmysqlclient15-dev

3. $which is mysql_config
Now you should get something like this.
/usr/bin/mysql_config

4.  sudo gem install mysql
 or $sudo gem install mysql -- --with-mysql-config = /usr/bing/mysql_config

Gem files will remain intsalled in /var/oib/gems/1.9.0/gems/mysql-2.8.1/ for inspection
 extconf.rb:1:in 'require': no such file to load - mkmf (LoadError)
If you get the above error, you may have to install ruby1.8-dev or ruby1.9-dev.

sudo apt-get install ruby1.8-dev
sudo apt-get install ruby1.9-dev

5. ln -s /var/run/mysqld/mysqld.sock /tmp/mysql.sock
Run the above command if you get the error message below.
sudo / -name mysqld.sock if you don't know where your sock file is.

/usr/local/lib/site_ruby/1.8/mysql/protocol.rb:212:in 'initialize': No such file or directory - /tmp/mysql.sock (Errno::ENOENT)
	from /usr/local/lib/site_ruby/1.8/mysql/protocol.rb:212:in 'new'
	from /usr/local/lib/site_ruby/1.8/mysql/protocol.rb:212:in 'initialize'
	from /usr/lib/ruby/1.8/timeout.rb:53:in 'timeout'
	from /usr/local/lib/site_ruby/1.8/mysql/protocol.rb:209:in 'initialize'
	from /usr/local/lib/site_ruby/1.8/mysql.rb:110:in 'new'
	from /usr/local/lib/site_ruby/1.8/mysql.rb:110:in 'connect'
	from /usr/local/lib/site_ruby/1.8/mysql.rb:42:in 'connect'
	from mysql.rb:2

6. Example

6.1 mysql>CREATE TABLE EMP(EMP INT, ENAME VARCHAR(20));
    mysql> INSERT INTO EMP(EMP,ENAME) VALUES(1,'Tom Luo');
 
6.2

vi mysql.rb

require 'mysql'
my = Mysql.connect('localhost', 'user', 'password', 'database_name')
 my.query("select EMPNO,ENAME from EMP").each do |EMPno,ENAME|
   p EMPNO,ENAME
 end
 stmt = my.prepare('insert into EMP(EMPNO,ENAME) values (?,?)')
 stmt.execute 2, 'Robert Martin'

7. Test in irb
irb>require 'mysql'
irb>my=Mysql.connect('localhost','user','password','db_name')
irb>my.query("SELECT log2(1024) FROM DUAL").each {|x| puts x}
10
irb>my.query("SELECT radians(180) FROM DUAL").each {|x| puts x}
3.14159265358979

Now you can call any MySQL functions. LOG2 is a MySQL function that is missing in Ruby.

See this page for more examples.
http://www.tmtm.org/en/mysql/ruby/example.html