Apparently is it because the socket file got moved during the update [http://www.macosxhints.com/article.php?story=20060111113313511]. To repair this problem, open the Terminal and enter the following commands:
The first line is creating a folder called "mysql" inside the "var" folder at the root level, the second line is making a link called "mysql.sock" to the actual "mysql.sock" file (at the changed location) inside the invisible "tmp" folder.$ sudo mkdir /var/mysql
$ sudo ln -s /tmp/mysql.sock /var/mysql/mysql.sock
Do this and you should be fine again.
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