The elements in a relational database are organized into tables, with rows and columns. They are the right choice for cases where data integrity is very important (ACID compliant).
Examples: MySQL, Microsoft SQL Server, PostgreSQL, Oracle
They have become an alternative to relational ones as web applications have become more and more complex. They are agnostic in terms of the scheme used, allowing unstructured or semi-structured data to be stored and manipulated.
● Key-Value Stores: Redis, Amazon DynamoDB
● Wide-Column Stores: Cassandra, Apache HBase
● Document Stores: MongoDB, Couchbase
● Graph Databases: Neo4j