Relational databases

A relational database organizes data into tables. Data in one table can link to data in other tables to create relationships—hence, the relational part of the name.

A table stores data in rows and columns. A row, often called a record, contains all information about a specific entry. Columns describe attributes of an entry. The following image is an example of three tables in a relational database.

The preceding image shows a table for books, a table for sales, and a table for authors. In the books table, each row includes the International Standard Book Number (ISBN), title, author, and format. Each of these attributes is stored in its own column. The books table has something in common with the other two tables—the author attribute. That common column creates a relationship between the tables.

The tables, rows, columns, and relationships between them is called a logical schema. With relational databases, a schema is fixed. After the database is operational, it becomes difficult to change the schema. Because of this, most of the data modeling is done up front before the database is active.

Relational database management system

With a relational database management system (RDBMS), you can create, update, and administer a relational database. Some common examples of RDBMSs include the following:

• MySQL

• PostgresQL

• Oracle

• Microsoft SQL Server

• Amazon Aurora

You communicate with an RDBMS by using structured query language (SQL) queries, similar to the following example:

SELECT \ FROM table_name*.

This query selects all the data from a particular table. However, the power of SQL queries is in creating more complex queries that pull data from several tables to identify patterns and answers to business problems. For example, querying the sales table and the books table together to see sales in relation to an author’s books. Querying tables together to better understand their relationships is made possible by a "join".

Choose between unmanaged and managed databases

If you want to trade your on-premises database for a relational database on AWS, you first need to select how you want to run it—managed or unmanaged. Managed services and unmanaged services are handled similar to the shared responsibility model. The shared responsibility model distinguishes between AWS security responsibilities and the customer’s security responsibilities. Likewise, managed compared to unmanaged can be understood as a trade-off between convenience and control.

Unmanaged databases

If you operate a relational database on premises, you are responsible for all aspects of operation. This includes data center security and electricity, host machines management, database management, query optimization, and customer data management. You are responsible for absolutely everything, which means you have control over absolutely everything.

Now, suppose you want to shift some of the work to AWS by running your relational database on Amazon Elastic Compute Cloud (Amazon EC2). If you host a database on Amazon EC2, AWS implements and maintains the physical infrastructure and hardware and installs the EC2 instance operating system (OS). However, you are still responsible for managing the EC2 instance, managing the database on that host, optimizing queries, and managing customer data.

This is called an unmanaged database option. In this option, AWS is responsible for and has control over the hardware and underlying infrastructure. You are responsible for and have control over management of the host and database.

You are responsible for everything in a database hosted on-premises. AWS takes on more of that responsibility in databases hosted in Amazon EC2.

Managed databases

To shift more of the work to AWS, you can use a managed database service. These services provide the setup of both the EC2 instance and the database, and they provide systems for high availability, scalability, patching, and backups. However, in this model, you’re still responsible for database tuning, query optimization, and ensuring that your customer data is secure. This option provides the ultimate convenience but the least amount of control compared to the two previous options.