Can you name the main types of databases and their features?

Main types of databases and their features:

1. Relational Databases (SQL)

   • Store data in tables with a clearly defined schema.
   • Use SQL language for queries.
   • Provide transactions and data integrity.
   • Examples: MySQL, PostgreSQL, Oracle.

2. Document-oriented Databases (NoSQL)

   • Store data as documents (usually JSON-like).
   • Flexible schema, easily scalable.
   • Suitable for storing unstructured data.
   • Examples: MongoDB, CouchDB.

3. Key-Value Stores

   • Very simple model: a key associated with a single value.
   • High performance and scalability.
   • Used for caching and sessions.
   • Examples: Redis, Riak.

4. Graph Databases

   • Store data as nodes and edges.
   • Suitable for complex relationships, e.g., social networks.
   • Examples: Neo4j, JanusGraph.

5. Columnar Databases

   • Store data by columns, not rows.
   • Efficient for analytical queries.
   • Examples: Apache Cassandra, HBase.

The choice of database depends on requirements for data structure, volume, speed, and query type.