PostgreSQL vs MySQL
MySQL and PostgreSQL are open source RDBMS, but Oracle « owns » the main fork of MySQL.
PostgreSQL has traditionally focused on reliability, data-integrity and integrated developer-focused features. It has a sophisticated query planner, capable of joining large numbers of tables efficiently. MySQL, on the other hand, has traditionally focused on read-mostly web applications where the principal concern is the query optimisation.
PostgreSQL supports most of Oracle's syntax which is not the case for MySQL.
PostgreSQL has a better support for SQL and a better query optimizer. This databasae is a good fit for applications that need ad-hoc querying.
PostgreSQL has only one storage engine while MySQL has nine of them.
In MySQL, MyIsam is the initial storage engine. It was built for speed (no transactions): it uses table locking. InnoDB is currently the default storage engine in MySQL. It has transactions and it is also faster than MyIsam. InnoDB storage engine is adapted for customer-facing applications while PostgreSQL is more adapted for data-minning and warehousing as it needs a garbage collector.
TABLE SAMPLE to quickly retrieve a sample of an entire table. This supports filtering using
WHERE clauses. It is a valuable feature for data visualisations.
GIST indexes to quickly query sets of Cartesian coordinates and to get the nearest neighbors to any point.
MySQL has a C/C++ plugin API. PostgreSQL supports many programming languages, including C/C++, Java, .Net, Perl, Python, Ruby. It also allows to run user-supplied code as background workers.
Full text search is available in InnoDB from MySQL 5.7.3.