What is the difference between MySQL and MongoDB?

MySQL is a relational database management system that uses a tabular data structure based on SQL. Data is stored in tables with strict definitions of columns and relationships between them.

MongoDB is a document-oriented NoSQL database management system. Data is stored as documents in BSON format (binary JSON), which are grouped into collections. The document structure can be flexible.

Main differences:

Characteristic	MySQL (Relational)	MongoDB (NoSQL, Document-oriented)
Data model	Tables, rows, columns. Strict schema.	Documents (BSON), collections. Flexible schema (schema-less).
Query language	SQL (Structured Query Language)	MongoDB Query Language (based on JSON).
Scaling	Vertical (increasing server capacity), horizontal (more complex, sharding required).	Horizontal (easier, built-in replication and sharding mechanisms).
Data relationships	Explicit, defined by foreign keys and JOIN operations.	Implicit, nested documents or references to other documents.
ACID transactions	High support for ACID properties (Atomicity, Consistency, Isolation, Durability).	Limited/different support for ACID, especially for distributed transactions.
Typical use cases	Applications with complex data relationships, ERP systems, financial systems.	Applications with flexible data structures, log collection, IoT, caching, CMS.

MySQL is suitable for applications requiring strict data integrity and complex relational queries. MongoDB is suitable for applications requiring high performance, schema flexibility, and horizontal scaling.