SUMMARY

Databases are common building blocks of applications, especially web-based applications. Most database systems are based on the concepts of relational database theory, so you can expect most problems you encounter to involve accessing and manipulating relational data. To do this, you need to understand basic SQL commands such as SELECT and INSERT. Transactions and foreign key constraints are among the mechanisms that databases provide to maintain consistency. NoSQL concepts and questions also come up occasionally, as do properties of transactions and distributed databases.