A database dependency is a formal concept which is used to describe patterns in data. These patterns are employed during data analysis, data cleansing, and schema normalization. There is about dozen of major dependency types. In this paper we survey these types of database dependencies employed in the relational databases. We start from the earliest ones - functional dependencies and conclude with the state-of-the-art findings. For each type we provide both formal and non-formal definitions and present an example and counterexample. We also briefly discuss extraction algorithms and possible use cases.