May 30th, 2020 
These are nothing but the APIs of PHP that is used to access the MySQL databases and tables. The developers can choose either one of them for their project, however, the use of MySQL extension is deprecated and will not be available in future versions. It is recommended to use the MySQLi extension with PHP 5.5 and above.
Let’s have some more information about each of them:
MySQL: This was the main extension that was designed to help PHP applications send and receive data from the MySQL database. However, the use of MySQL has been deprecated and removed as of PHP 7 and its newer versions. This is why it is not recommended for new projects, and that’s the reason why MySQLi extensions are used more nowadays.
MySQLi: The ‘i’ in MySQLi stands for Improved. Therefore, this is also known as the improved version of MySQL. It has many useful features.
- An Object-oriented interface
- Support for prepared statements
- Support for multiple statements
- Support for transactions
- Enhanced debugging capabilities
- Embedded server support.
