SQL vs NoSQL Databases: Understanding the Key Differences

SQL and NoSQL are mainly databases. SQL is a relational database and NoSQL are non-relational databases. It is important to note that NoSQL databases do not mean “No to SQL”, it means “not only SQL”. Both these databases do the same thing, which is store data. They are different primarily in the way they store data. They are both relevant today and have their own uses. Neither is superior to the other, it’s just the way that these databases are used that make them most relevant to a particular purpose. 

Examples of SQL database are MySql, Oracle, Sqlite, Postgres and MS-SQL. Some of the popular NoSQL database are MongoDB, BigTable, Redis, RavenDb, Cassandra, Hbase, Neo4j and CouchDb. 

As you read further in this post, bear these images in mind for better recall. These images will also act like a quick guide to understand the differences between SQL and NoSQL. Let’s see what these differences are:-

Data Storage

The very basic and important difference between the two databases is the way data is stored. A relational database or SQL database has structured storage, while a non-relational database or NoSQL allows a free flow. What does this mean?

SQL databases are fixed in their approach to structuring the data stored, say for instance, like a phone book. A phone book has the contact details of a person and nothing beyond. Of course, it can have multiple phone numbers, but it is still phone numbers that follow a pattern, like the number of digits that are generally fixed. NoSQL database, on the other hand, has a more open approach to data. It allows room for adding different flavors of information. Most importantly, the additional information can be included as and when procured.

Continuing the example of a phone book in a NoSQL database, the data stored will be more than just the contact numbers. It will allow additional information like postal address, email ID, social media details, inputs from the web behavior like photo sharing, geographical information, online activity, usage metrics and so on. 

Schema

Schema is the technical way of saying the organization of the structure of a database. An SQL database is organized in the form of tables with columns and rows. They are all pre-defined and have specific relationships. This whole thing is called the schema. A schema that is well-defined reduces data redundancy. It keeps the tables relevant for a long period of time. The flip side is it doesn’t allow modifications. Any modifications will mean redefining the whole schema. In the case of an SQL database, this is how the schema works. Yes, it is rigid. 

A NoSQL database is for unstructured and dynamic data. The schema for these databases is also dynamic and not rigid.

Scalability

SQL databases restrict the data to certain parameters while NoSQL databases do not. In an SQL database, the columns are fixed. The rows can extend to any number that the hardware used supports, like the CPU, RAM and SSD. In this sense, the scalability of an SQL database is vertical. 

A NoSQL database allows unrestricted data updates. The data updates are not necessarily in the same line of information too. For instance, there can be a picture, a comment, a pool of text, an email ID and so many other aspects. To accommodate such data, a NoSQL database needs more servers. In this sense, these databases are horizontally scalable. 

Queries

SQL databases are driven by Structured Query Language for its data needs. You will to follow the specific syntax applicable to this language. In a NoSQL database, there is no such limitation as these databases are queried on collection of documents. The syntax will change from one database to another. 

SQL databases are also designed for complex queries, whereas NoSQL databases are not. 

ACID Compliance

Atomicity, Consistency, Isolation, and Durability (ACID) are important features of data for some businesses like the financial sector. ACID compliance outlines the interaction of a transaction with a database. It reduces mistakes and retains data integrity. SQL databases offer ACID compliancy, unlike the NoSQL databases, owning to their dynamic nature. 

Fast Paced Operations

SQL databases will not be a good fit in a business that is fast-paced and rapidly changing. These databases are not agile to fit the requirements of such a business. A NoSQL database on the other hand, will be an ideal match for such businesses. 

Both the databases have their pros and cons. While SQL databases are not flexible, they are highly reliable for complex querying. On the other hand, NoSQL databases rank high on flexibility but low on complex querying. Both of them have their uses in a particular environment. The more well-defined the environment, the easier it is, to choose the ideal database between SQL and NoSQL.