MySQL is the most popular relational database which is free to use. It is normal for many of the MySQL users to think – why we will learn MongoDB or any noSQL? Typically, MongoDB is for a different type of applications to meet today’s need. You can think the visitor tracking plugin for your WordPress website using MongoDB. It is not a good use-case of MongoDB, but probably points where MongoDB can be co-used.
How MongoDB Differs From MySQL
MySQL is one king of the relational databases. None going to compete with MySQL for its suitable use-cases. Any type of application which requires multi-row transactions would better suit a relational database. Accounting software is a good example of such. MySQL allows us to interact with the database which are using the structured query language. PostgreSQL, Microsoft SQL Server is other good software which can handle SQL as a query language. SQL is quite powerful. That brings the disadvantages as some queries require the data to be stored on the same server else the query would be slower. That makes MySQL commands difficult to decipher by a newbie!
MongoDB is too much limited. First, the data size in MongoDB will be higher as each document has field names stored it. There are no JOINs, so it is less flexible. You need something like Hadoop to work with real Big Data. You can not compare the huge documentation of MySQL with MongoDB.
The above screenshot is from extensive research by Dmitry Dolgov.