Tapan Chudasama

Databases are used by almost all application that we create. If you want your application to store data at some point, then database is a must. But then the question arises which database to use, SQL or NoSQL?

What are SQL databases?

SQL databases are traditional databases that everyone has a picture of in their minds. It has rows and columns. Generally, each row represents an entity and each column of the row represents some attribute of the entity. For example: Consider this table1.

Here, Employee_Name,Age and Employee_ID are attributes of each Employee.

Let's us consider a second example. Consider this table2.

Now, let's say you want to get all the names of people who are at the position of Tech Lead. Note that the second table does not have the names of the Employees, but only Position. So you'll have to perform JOIN between two tables. Both the tables have one column common: Employee ID. So the query you need is-

SELECT t1.Employee_Name, t2.Position,

FROM table1 t1

INNER JOIN table2 t2

ON t1.Employee_ID=t2.Employee_ID

WHERE Position="Tech Lead"

There result of this query will be:

Thing to note here is that Employee_ID attribute links both the tables together and establishes a relation between them. So SQL databases re also called RDBMS (Relational Database Management Systems).

What are NoSQL databases?

NoSQL databases are different from SQL databases in way that they don't store data in a traditional row and column format. But in a key-val format or document-oriented format or graph-based format. For example: MongoDB, an example of NoSQL database, stores data in the form of documents in the database.

But before creating a database, MongoDB creates a cluster and within this cluster, it creates multiple databases. Within each database, you have multiple documents (collection) and in each document, lies your data.

Cluster (has) -> Databases (have) -> Collection of Documents (have) -> Data.

Each document has some data that is stored in the form of JSON. An example of JSON would be

So each person in the document is a JavaScript Object. So the entire table1 if stored in MongoDB would look like this.

Each employee is a JSON object and each object has some fields associated with it. Now, if you want to query some data in the document, the query would go like:

db.employeedata.find( { "position" : "Tech Lead" } )

Here employeedata is the name of the collection where our data is stored. This query is equivalent to the SQL query above.

Thing to note here is that as data is stores in JSON format, adding a value becomes easy. For example, If you want to add attribute End Date of internship for Mary Jane, so the table becomes:

Same goes for deletion. If you delete the Salary field from Mary Jane, the entire database does not get affected. But in case of SQL, if you want to delete Salary of a entity, you have to delete Salary for all the entities.

Differences between SQL and NoSQL

Conclusion

• If you want to develop a application that will be storing sensitive data or any other application where you think that data should be consistent throughout the database (ACID properties), you should go for SQL database. That is why databases used by banking applications, Air Ticket booking websites and other online booking sites always use SQL.
• If you are developing a application where security is not a issue, or you expect that user is not going to perform complex queries such as JOINS, or maybe just you want to have a flexible schema for database, go for NoSQL database. That is why database used by EA Sports for storing the user preferences and user data, is NoSQL.