Pls I wnt to generate a unique random num (not saved in MySQL) using either JavaScript or PHP, should b saved in MySQL database.

Answer 1

UUID means 'universally unique identifier'. It is precisely what you described, a commonly applied technique to generate large unique random numbers.
Typically there are built-in data types and functions to generate this in most programming languages. You can even delegate the creation to MySQL natively, with the built-in uuid() function. I would prefer this option. But if you want to do it in another language, you can research how to do that.

https://dev.mysql.com/blog-archive/storing-uuid-values-in-mysql-tables/

Answer 2

"Pls I want to generate ... (not saved in MySQL) ... , should be saved in MySQL database"

Is it to be saved in database or not? I suggest you to fix the post title to be clear about whether or not to save that random number ...