Are you still putting your data in plain, old spreadsheets? Excel 2013 makes it easy to link tables, create reports and more.

Excel possesses formidable database powers. Creating a relational database starts with a Master table that links to subordinates called (awkwardly) Slave, Child, or Detail tables.

Creating and using an SQLite database for data persistence in Android apps. Covers the basics, as well as using foreign keys. Full source included.

However, it is often necessary to defer constraint enforcement - during a database migration for example or loading a relational schema with cyclic foreign key dependencies.