Drush does not work on my Mac I use MAMP on Mac.

When I try to use drush en omega command on drupal root directory to install omega, But the terminal throw me an error: 

drupal-7.23 tangmonk $ drush en omega

Command pm-enable needs a higher bootstrap level to run - you will   [error]
need to invoke drush from a more functional Drupal environment to run
this command.

The drush command 'en omega' could not be executed.                  [error]
Drush was not able to start (bootstrap) the Drupal database.         [error]

Hint: This may occur when Drush is trying to:
 * bootstrap a site that has not been installed or does not have a
configured database. In this case you can select another site with a
working database setup by specifying the URI to use with the --uri
parameter on the command line. See `drush topic docs-aliases` for
details.

Drush was attempting to connect to:
 Drupal version         :  7.23
 Site URI               :  http://default
 Database driver        :  mysql
 Database username      :  root
 Database name          :  drupal
 Default theme          :  garland
 Administration theme   :  garland
 PHP executable         :  /usr/bin/php
 PHP configuration      :
 PHP OS                 :  Darwin
 Drush version          :  7.0-dev
 Drush configuration    :
 Drush alias files      :
 Drupal root            :  /Users/tangmonk/Sites/drupal/drupal-7.23
 Site path              :  sites/default
 File directory path    :  sites/default/files
     * connect the database through a socket. The socket file may be
    wrong or the php-cli may have no access to it in a jailed shell. See
    http://drupal.org/node/1428638 for details.


It seems mysql issue. But my site run perfect.
I run drush command as MAMP Integrated PHP, It works!

I add alias command to my shell:

$ vim ~/.bash_profile
alias drush='/Applications/MAMP/bin/php/php5.5.3/bin/php /opt/drush/drush.php'