I have heavily worked on the MongoDB NoSQL Database and oracleOracle.
Schema
SQL database has its own predefinepredefined schema to store structurestructured data.
In NoSQL database, there is no predefinepredefined schema, here schema is most dynamic element based on the data elements.
Scalability
SQL Databases are vertically scalable, which means if we want to scale SQL base database, we need to give hardware boost on which the DBMS System is installed. This is where it sometimes goes for the limitation of scalability.
NoSQL databasedatabases are horizontally scalable, means if we want to scale it, we need to add more nodes and create distribution network based on our own need and required power. This is how itthey reduce load on the database
Data Retrieval
In SQL based databasedatabases, to define and manipulate data we can use SQL (StructureStructured Query Language), which is very powerful now a daysnowadays.
In terms of NoSQL database, queries are focus on the collection and documents. Sometimes it is called as UnQL (Unstructured Query Language). This is still in the evolution phase, so it is varies from vendor to vendor of the NoSQL database.
For more on key differencedifferences, my blog: hereDifference between SQL and NoSQL database