SQL vs NoSQL

So after reading about SQL and NoSQL, the common questions that comes in mind are

What are the differences between the two ?

When do we choose SQL over NoSQL or vice-versa ?

What are the properties needed to decide the type of datastore to use in your application ?

Differences

• SQL databases are not suitable for hierarchical data storage while NoSQL databases are.

• SQL supports ACID, while NoSQL doesn't.

• SQL databases support Joins, while NoSQL joins can only be achieved at application layer.

• SQL Databases are strongly consistent, while NoSQL databases are highly available.

• SQL databases are preferred when the requirement is of correct and consistent data, while NoSQL databases rely on fast data and can compromise on accuracy

• SQL databases are vertically scalable while NoSQL are horizontally scalable.

Criteria	SQL/NoSQL
High number of reads/writes (High QPS)	NoSQL
High Concurrency	NoSQL
Low Reads/Writes (Few thousands per second)	SQL
Joins Needed	SQL
Strong Consistency	SQL
High Availability	NoSQL
Transaction Properties	SQL
High Commodity Hardware (Vertically Scalable)	SQL
Low Commodity Machines (Horizontally Scalable)	NoSQL
Sharding	NoSQL
Partitioning	SQL

Partitioning: Partitioning is dividing large data into multiple tables in a single database. Vertical partitioning is dividing data by columns into multiple tables (normalisation), while horizontal partitioning is dividing data by rows into multiple tables.

Sharding: Sharding is dividing large data into smaller chunks across multiple machines. There are two types of sharding: Vertical sharding where the data is divided by columns across machines where horizontal sharding is dividing data by rows across machines.

For More Reading

• SQL vs NoSQL