MySQL

An index is a sorted data structure that lets MySQL find rows without scanning the entire table. The right indexes can turn a slow query into an instant one.

Relational databases split data across multiple tables to avoid repetition. JOINs let you recombine that data in a single query.

Choosing the right data type for each column saves storage space, enforces data integrity, and keeps queries fast.

SQL (Structured Query Language) is how you read and write data in MySQL. The four basic operations (SELECT, INSERT, UPDATE, DELETE) cover the vast majority of day-to-day work.

MySQL is the world's most popular open-source relational database. It stores data in tables with rows and columns, and you query it using SQL.