Comment 3 for bug 234609

Moodle uses either mysql or pgsql as it database backend. Since you have installed php5-pgsql, it does'nt install php5-mysql as part of its dependency.

Also after the configuration screen where you get to select the database,username,password, etc., you will be warned that the script cannot connect to the server (Failed to connect to database: Can't connect to local MySQL server through socket...)