[NOISE] When you build an aggregation with PHP 99% of 0:00 the time you'll be interacting with some sort of data store. 0:04 And this is very often an SQL database. 0:09 SQL stands for structured query language. 0:12 If you're unfamiliar with SQL databases, you should check out the course, 0:15 database foundations. 0:19 SQL databases allow you to save users, blog posts, 0:22 payment information, and whatever else your website will need to remember, and 0:25 provides you with an interface to fetch that data back whenever you need it. 0:28 There are many options for 0:31 working with databases in PHP, such as MySQL, PostgreSQL, and SQLite. 0:34 MySQL is incredibly popular with the PHP community. 0:39 But if you end up using that, you have to be careful. 0:41 There are three extensions that can be used to connect to 0:45 MySQL databases and PHP. 0:48 MySQL, MySQLI, and PDO. 0:50 The MySQL extension is currently deprecated, and 0:53 will be removed from the upcoming version of PHP. 0:56 You shouldn't use this for anything anymore. 0:59 MySQLI and PDO are the only remaining safe options. 1:01 If you are not using MySQL and decide to go with another popular system, 1:04 like Postgres or SQL Lite, then there are extensions for 1:07 that too, such as PGSQL, SQLite, and also PDO. 1:10 If you are unsure which to use, a sensible option is to always work with PDO. 1:15 PDO allows you to learn one PHP API for interacting with many supported databases. 1:20 This allows you to use the same API to interact with MySQL, Postgres, and SQLite, 1:25 or many others without having to relearn a brand new set of functions and classes. 1:30