Understand the principles of relational databases and learn basic SQL queries with systems like MySQL or PostgreSQL.
Relational databases are a mature and robust technology for data storage, based on the relational model. They organize data into tables, which are composed of rows and columns. Each table has a predefined structure, known as a schema, that dictates the data type and constraints for each column. This strict schema ensures data consistency and integrity. The 'relational' aspect comes from the ability to define relationships between tables. For example, in an e-commerce application, you might have a `users` table and an `orders` table. A relationship can be established between them using a 'foreign key', where an `order` row contains a `user_id` that points to the corresponding row in the `users` table. This allows for powerful and efficient querying of related data. The language used to interact with these databases is SQL (Structured Query Language). SQL is a declarative language used for creating, reading, updating, and deleting data (CRUD operations). We'll cover fundamental SQL statements: `CREATE TABLE` to define a schema, `INSERT` to add new data, `SELECT` to query data (including filtering with `WHERE` and joining tables with `JOIN`), `UPDATE` to modify existing data, and `DELETE` to remove data. MySQL and PostgreSQL are two of the most popular open-source relational database management systems (RDBMS). While they are largely similar, PostgreSQL is often favored for its more advanced features and closer adherence to SQL standards.