PHP is a web language based on scripts that allow developers to dynamically create generated web pages.

The following two rules are needed to be followed while naming a PHP variable:

• A variable must start with a dollar symbol, followed by the variable name. For example: $price=100; where price is a variable name.
• Variable names must begin with a letter or underscore.
• A variable name can consist of letters, numbers, or underscores. But you cannot use characters like + , – , % , & etc.
• A PHP variable name cannot contain spaces.
• PHP variables are case-sensitive. So $NAME and $name both are treated as different variables

• PHP scripts have the ability to generate HTML, and it is possible to pass information from HTML to PHP.
• PHP is a server-side language whereas HTML is a client-side language. So PHP executes on the server-side and gets its results as strings, objects, arrays, and then we use them to display its values in HTML.
• This interaction helps bridge the gaps and use the best of both languages

The 3 main types of errors in PHP are:

• Notices: Notices are non-critical errors that can occur during the execution of the script. These are not visible to users. Example: Accessing an undefined variable.
• Warnings: These are more critical than notices. Warnings don’t interrupt the script execution. By default, these are visible to the user. Example: include() a file that doesn’t exist.
• Fatal: This is the most critical error type which, when occurs, immediately terminates the execution of the script. Example: Accessing a property of a non-existent object or require() a non-existent file.

• require(), and require_once() perform the same task except that the second function checks if the PHP script is already included or not before executing it.
• (same for include_once() and include())

• To access the data sent this way, you use the $_POST array.
• Imagine you have a form field called ‘var’ on the form when the user clicks submit to the post form, you can then access the value like this:
• $_POST[“var”];

•  You need to change the value of the max_execution_time directive in the php.ini file for increasing the maximum execution time.
• max_execution_time = 120

The 4 main steps used to create a new MySQL database in PHP are given below:

• A connection establishment is done to the MySQL server using the PHP script.
• The connection is validated. If the connection is successful, then you can write a sample query to verify.
• Queries that create the database are input and later stored into a string variable.
• Then, the created queries will be executed one after the other

There are 4 ways of handling the result set of MySQL in PHP. They are:

• mysqli_fetch_array(): Returns the current row of the result set as an associative array, a numeric array, or both.
• mysqli_fetch_assoc(): Returns the current row of the result set as an associative array.
• mysqli_fetch_object(): Returns the current row of a result set, as an object.
• mysqli_fetch_row(): Returns result row as an enumerated array

The goto statement can be placed to enable jumping inside the PHP program. The target is pointed by a label followed by a colon, and the instruction is specified as a goto statement followed by the desired target label.