Make optimization to SQL query with SQL Server Management Studio

Writing SQL queries can be considered by some as a form of art: everyone has a different style of writing and improving them (I’m talking about complex queries). Queries can achieve the same goal while being written in various and sometimes completely different way. While improving and optimizing a query should first and foremost include making sure that everything is written correctly and there are no logical errors, I wanted to share a tool, that some of you might not know, which can help make queries more efficient in times where you’re just not sure how to improve it further.


Interview Question: Select only Prime numbers from table

As part of my daytime job, I conduct professional interviews for candidates. For that, I’m always on the search for good interview questions. I regard a good question if it’s not too complicated, has a number of ways to solve, and if needed, can be solved programmatically with SQL or C / C# / JAVA languages.

Now that I’m done with asking the prime number question (I need to change questions every now and then), I thought I will post the solution here.


Calculate average time from DateTime MySql

Calculating average time from DateTime field in MySql might come in handy in cases like getting the average arrival time, departure time, service sampling etc. In my case, I have a database with records on my arrival to work, and I wanted to calculate time average time that I arrive by the office, and then calculate how much time I spend in traffic, depending on when I leave my home.


Prevent cookie hijacking (session hacking)

First of all, what is “Cookie Hijacking”?

By Wikipedia, it’s an “exploitation of a valid computer session to gain unauthorized access to information or services in a computer system. In particular, it is used to refer to the theft of a magic cookie used to authenticate a user to a remote server”.

Which basically means, gaining access to an information system or a website without logging in, as the user that the cookie (or session) belongs to him.