JSON data can be stored as a column with optional indexes. In 9.4 (upcoming at the time of this writing), JSONB will be a binary version of JSON that will save space. It's like the best of the NO-SQL world without having to give up ACID and Relationships. This means that cascading deletes can be done in a single Transaction across multiple JSON documents.
PostgreSQL performance increases with each release, this is also proven by many benchmark tests.
Notable performance features include:
As PostgreSQL only supports one storage engine, it has been able to integrate and optimise it and with the rest of the database. This has resulted in multiple benefits such as the ability to allow different transaction types to co-exist efficiently without the need to select storage engine types once for each table ahead of time.
On the fly data compression resulting in less IO required for reading.
Asynchronous + synchronous Replication.
PostgreSQL supports a asynchronous API for use by client applications. It is reported to increase performance by up to 40% and is not supported by MySQL.
Designed to scale very well with large numbers of cores at high concurrency levels.
PostgreSQL is known to have a very holistic approach to robustness and data integrity which is reflected by it being fully ACID compliant.
PostgreSQL has always been strict about making sure data is valid before allowing it into the database, and there is no way for a client to bypass those checks.
Depending on your requirements, ACID compliance might be important.
An SQLite database is a single ordinary disk file that can be located anywhere in the directory hierarchy. It works by sending requests to a single file where all the data is kept instead of communicating with a hosted database which gives access to an interface by making use of sockets and ports. The file format used is also cross-platform, so can easily be migrated to various machines.
This makes SQLite extremely portable throughout different applications, all that's needed to transfer the whole database is to make a copy of the file.
Because of it's ability to scale and with the portability that a single-file database gives you without losing much of the power and features that SQL gives developers, it's a great choice for testing applications and for the early stages of development when the workload and the data that needs to be stored is not that large.
There is literally no configuration required to get SQL lite up and running. This is mainly due to SQLite being serverless, there is no separate server process to install, setup, configure, initialize, manage, and troubleshoot.
SQLite is made to be extremely lightweight and portable, but it still uses SQL. However, some SQL features such as RIGHT OUTER JOIN and FOR EACH STATEMENT are missing.
As MySQL is used by a lot of people, there's a good number of libraries, tutorials and examples available that should help you through all kinds of situations.
Because of it's popularity there are a lot of tutorials and guides out there that help developers install and work with MySQL. The installation process itself is not very hard and there are multiple powerful GUI tools that make it extremely easy to work with MySQL for a beginner.
Since MySQL is one of the most popular relational databases, maybe the most popular, there exist many third-party tools and applications that help developers to use MySQL in their development.
When you are trying to do something in MySQL and something goes wrong it will simply give you an error message with an error code. WHich does not say much about what went wrong unless you look it up online. This can be a little cumbersome during development.