Check similar text with MySQL and PHP

Please read ENTIRE description, otherwise you will be ignored (and I will NOT reply to you if you have not read the description). I need experienced PHP/MySQL developer who will create algorithm and code with PHP and MySQL for checking similarity percentage between text submitted via form against a number of texts stored in MySQL database. When the user submits the text the algorithm should return any entry in database with given percentage of similarity to the text submitted (you will compare only one column in database), e.g return all entries from database that have similarity > 40% with the text submitted by the user. E.g table TABLE - Articles id, article_body,article_title Code should return all rows that have similarity percentage > 40% (or other given value) with the text (article_body) the user have submitted. Only ONE column (the article_body column) will need to be compared. The algorithm must be as much as possible optimized. When you will write the code you will need to explain each line of both PHP and MySQL code. Exclusive and complete copyrights to all programming code will belong to me. You may not distribute the programming code in any way.