What is NoSQL?
The term “NoSQL Database” typically refers to a
non-relational database. NoSQL may stand for “Non-SQL” or “Not only SQL”. But
by considering the features of NoSQL, the most suitable term is “Not only SQL”.
Types of NoSQL databases
There are 4 major types of NoSQL databases.
1. Document
Database
2. Key
– Value Database
3. Column
Family Database
4. Graph Database
1. Document
Database
In Document databases, data is stored in documents
which is similar to JSON (JavaScript Object Notation) objects. Each document
may contain pairs of fields and values. Values may belong to the types like
strings, integers, booleans, arrays or objects. These databases are
horizontally scalable.
The most popular NoSQL database under document databases is MongoDB.
2. Key
– Value Database
Key – Value database is a simpler type database and
each item contains keys and values. A value can only be retrieved by referring
the key. In a situation where a large amount of data should be stored but no
need to perform complex queries to retrieve them, Key – Value databases may be
useful the most. (E.g.:- use cases)
The most popular NoSQL databases under Key – Value
databases are Redis and DynanoDB.
3. Column
Family Database
Column Family Database is also known as “Wide – Column
Database”. This database stores data in tables, rows, and dynamic columns. It
is not required to have the same column for each row. That feature provides
more flexibility to the Column Family Database. This database is very useful to
store large amount of data. It is commonly used to store Internet of Things
data and user profile data.
The most popular NoSQL databases under Column Family databases are Cassandra and HBase.
4. Graph
Database
In Graph Databases, data is stored in nodes and edges.
Information about people, places and things are stored in nodes while information
about the relationships between nodes are stored in edges.
The most popular NoSQL databases under Graph databases
are Neo4j and JanusGraph.
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