I'm attempting to appreciate this: If you will find errors within the database like FK issues, Missing tables/posts, or even when the database is dead -> Will this crash the applying? I've this site in php. How about application and network related errors? Can these cases be caught for and also have a deal with without customers visiting a non functionaning site or site lower message?

You will find a number of ways to identify errors and take care of them in PHP.

Exceptions, and check out-Catch claims.

Here's examples of both.

The way you catch database errors will rely on what type of database it's. If you are using MySQL, then PHP allows you catch query errors such as this. Here's the doc on die and mysql_error().

mysql_query( querystuff ) or die( mysql_error() );

Generally you should check each and every little bit of the application, from database connectivity to user input using php. That link assisted me a while ago http://www.nyphp.org/PHundamentals/7_PHP-Error-Handling It outlines try/catch error handling.