Turn off warnings and errors on PHP and MySQL

PHP error_reporting reference:

// Turn off all error reporting
error_reporting(0);

// Report simple running errors
error_reporting(E_ERROR | E_WARNING | E_PARSE);

// Reporting E_NOTICE can be good too (to report uninitialized
// variables or catch variable name misspellings ...)
error_reporting(E_ERROR | E_WARNING | E_PARSE | E_NOTICE);

// Report all errors except E_NOTICE
// This is the default value set in php.ini
error_reporting(E_ALL ^ E_NOTICE);

// Report all PHP errors (see changelog)
error_reporting(E_ALL);

// Report all PHP errors
error_reporting(-1);

// Same as error_reporting(E_ALL);
ini_set('error_reporting', E_ALL);

When you are sure your script is perfectly working, you can get rid of warning and notices like this: Put this line at the beginning of your PHP script:

error_reporting(E_ERROR);

Before that, when working on your script, I would advise you to properly debug your script so that all notice or warning disappear one by one.

So you should first set it as verbose as possible with:

error_reporting(E_ERROR | E_WARNING | E_PARSE | E_NOTICE);

UPDATE: how to log errors instead of displaying them

As suggested in the comments, the better solution is to log errors into a file so only the PHP developer sees the error messages, not the users.

A possible implementation is via the .htaccess file, useful if you don't have access to the php.ini file (source).

# Suppress PHP errors
php_flag display_startup_errors off
php_flag display_errors off
php_flag html_errors off
php_value docref_root 0
php_value docref_ext 0

# Enable PHP error logging
php_flag  log_errors on
php_value error_log  /home/path/public_html/domain/PHP_errors.log

# Prevent access to PHP error log
<Files PHP_errors.log>
 Order allow,deny
 Deny from all
 Satisfy All
</Files>

Always show errors on a testing server. Never show errors on a production server.

Write a script to determine whether the page is on a local, testing, or live server, and set $state to "local", "testing", or "live". Then:

if( $state == "local" || $state == "testing" )
{
    ini_set( "display_errors", "1" );
    error_reporting( E_ALL & ~E_NOTICE );
}
else
{
    error_reporting( 0 );
}

Prepend functions with the '@' symbol to suppress certain errors, as opposed to turning off all error reporting.

More information: http://php.net/manual/en/language.operators.errorcontrol.php

PHP supports one error control operator: the at sign (@). When prepended to an expression in PHP, any error messages that might be generated by that expression will be ignored.

@fsockopen();