How PHP avoids the data submitted by the form is safe

How PHP handles the data submitted by the form is safe
What needs to be done with user-submitted form data to prevent js,sql injection, prevent duplicate commits and commit illegally
What to do to filter out the submitted illegal data, hope to have a complete code, thank you.

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This reads "PHP and MySQL Web development" can be mastered by the system.

JS anti-injection: Htmlspecialchars
SQL anti-injection: mysql_real_escape,addslashes
Filter illegal data: Must own coding the check rule, you want how to examine to write the code yourself, with regular, with Trim,isset,empty, and so on.
Prevent illegal submissions: their own coding, the order is isset,trim,empty, other checks, roughly this order.
Repeat commit: Generate a unique ticket in the session and add ticket to the hidden of the form, and the validation is consistent after the form is submitted.

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