MySQL VS mysqli, which one should I use? What to do with it

MySQL VS mysqli, which one should I use?
Beginner PHP, see the database here
The textbook says mysqli is a new extension that has been improved on MySQL extensions:
Self-binding/preparation/execution functions
Pointer support
Multi-statement support
......
Ask colleagues, they are basically using MySQL rather than mysqli, do not know why?

The talent to explain?

Thank you!

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Pdo
!
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It's like MySQL, right?
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The latest version of PHP has to be abandoned MySQL.
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MySQL function group is a process-oriented set of functions based on MYSQL4 development
mysqli function Group is an object-oriented set of objects developed based on MYSQL5
To cater to the needs of older programs, MYSQLI also provides process-oriented functions

We recommend using PDO form MySQL

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