When you import data into a PostgreSQL database, the sequences are not updated automatically. In the PostgreSQL wiki there is a guide showing you how to update the sequences to the max value of the id column by generating a query for each table.
Here is the full guide: Fixing Sequences
If you use XAMPP for your MySQL and you want to use another program to manage your database instead of phpMyAdmin, for example MySQL Workbench, you will need to allow remote access to MySQL.
Here is how from an answer in serverfault.com: How do I allow remote access to mysql using xampp?
This very helpful little guide shows how to export your excel data into a csv file and then import them to MySQL using a command. I’ve used it many times in the past and I keep it handy in my bookmarks.
Read the full guide here: Import Excel Data into MySQL in 5 Easy Steps
This article from J.P.Lewis and Ulrich Neumann contains some benchmarks between Java and C++. It is a little old (2004) but the results are very interesting.
Read more: Performance of Java versus C++