NoSQL (“non SQL” or “not only SQL”) databases were developed in the late 2000s with a focus on scaling, fast queries, allowing for frequent application changes, and making programming simpler for developers. Relational databases accessed with SQL (Structured Query Language) were developed in the 1970s with a focus on reducing data duplication as storage was much more costly than developer time. SQL databases tend to have rigid, complex, tabular schemas and typically require expensive vertical scaling.
Here are some main differences between SQL and NoSQL databases.
| SQL Databases | NoSQL Databases | |
|---|---|---|
| Data Storage Model | Tables with fixed rows and columns | Document: JSON documents, Key-value: key-value pairs, Wide-column: tables with rows and dynamic columns, Graph: nodes and edges |
| Development History | Developed in the 1970s with a focus on reducing data duplication | Developed in the late 2000s with a focus on scaling and allowing for rapid application change driven by agile and DevOps practices. |
| Examples | Oracle, MySQL, Microsoft SQL Server, and PostgreSQL | Document: MongoDB and CouchDB, Key-value: Redis and DynamoDB, Wide-column: Cassandra and HBase, Graph: Neo4j and Amazon Neptune |
| Primary Purpose | General purpose | Document: general purpose, Key-value: large amounts of data with simple lookup queries, Wide-column: large amounts of data with predictable query patterns, Graph: analyzing and traversing relationships between connected data |
| Schemas | Rigid | Flexible |
| Scaling | Vertical (scale-up with a larger server) | Horizontal (scale-out across commodity servers) |
| Multi-Record ACID Transactions | Supported | Most do not support multi-record ACID transactions. However, some—like MongoDB—do. |
| Joins | Typically required | Typically not required |
| Data to Object Mapping | Requires ORM (object-relational mapping) | Many do not require ORMs. MongoDB documents map directly to data structures in most popular programming languages. |
