Most high-performance non-relational databases (sometimes referred to as “not just SQL”) can also handle data with complex structures. However, they are not tied to fixed data models like relational databases (SQL).
Here are the four most common types of NoSQL databases:
Key-value
In key-value type stores, key and value pairs are generated using a hash table. Key-value type databases are best suited for when the key is known but the associated value is not.
Document databases
Document databases are an extended version of key-value databases in which entire documents are organized into groups called collections. They support nested key-value pairs and queries on any attributes of documents.
Column-based databases
Columnar, wide column, or column family based databases provide efficient data storage and querying of rows of sparse data. They are also convenient to use for querying specific columns of a database.
Graph
Graph databases use a model based on nodes and edges that represent related data (e.g., relationships between people in a social network). They also simplify storage and navigation of complex relationships.