September 30, 2014

Lessons I learned from SQL Interview

So today I had a technical interview with a company in Seattle. It was my first technical interview after two months of job hunting in the west coast. I am writing this posts to remember what I made a mistake in SQL as people usually say we learn lessons from mistakes and failure. 

First, About the rule that "GROUP BY function only allows you to SELECT two columns at a time". 
Remark: This does NOT include the new column you generate by using COUNT!!
Typical way you write a query with GROUP BY is like this:

SELECT Column1, Column 2 FROM TableName
GROUP BY Column1; 

HOWEVER, if you want to COUNT something else besides Column 1 and Column 2, you can write:

SELECT Column1, Column2, COUNT(Column3) 
FROM TableName
GROUP BY Column 1; 
SQL will not generate the errors when you put the third elements "COUNT(Column3) before "FROM TableName GROUP BY Column1" because "COUNT(Column3)" is not considered as the third column in the "GROUP BY". 

How about if you use JOIN to make it more complex. Then your query would be:
SELECT Table1.Column1, Table2.Column2, COUNT (Table2.Column3))
FROM Table1 JOIN Table 2 
ON Table1. Primarykey = Table2. Foreignkey
GROUP BY Column1; 

The reasons why you might better use Table1.Column1 instead of Column1 in this query when you have two tables is that the names of two columns in two tables might be the same. 

Second, About the data type of the date
Remember as the data type of the date is VARCHAR which means characters, you cannot use WHERE Date = 2004 to select the years. Assuming that the date in the table would be like "01-JAN-2004". You should write the query:
SELECT Column1, Column2 FROM Table1
WHERE Date LIKE "%2004" ; 

A little bit about the interview process:
The interviewer first asked me about a few questions about Tableau. For example: If I have performance issues with Tableau? If I have experience sharing the dashboard online with other people? How can I get the data from outside resource to Tableau? How can I connect two data at the same time in Tableau? How to change the data format when I upload the workbook to the public profile? 
Then we came to the chatting board to start the SQL questions. I listed the lessons I learned from the interview above. 

All the best to college students like me in the job market : ) 











September 28, 2014

Why did I create www.evafeng.com?

Inspired by a lot of excellent professionals in the data visualization field, I created the site to document the my path of exploring the data viz world. My old site was evasdatavisualization.weebly.com. At first, the old site was created only for presenting my projects in class. After I attended the Tableau Annual Conference 2014, I had a lot of inspiration and determination in creating my new site. I felt very lucky to get the domain name same as my name. I tried very hard to figure out the name of my new site. 

The named of the site is "Explore Viz Achieve". Did you notice that the initials of these three words are "E.V.A.", which is my name Eva? The name of the size is a snapshot of what I wanted to do in my career: 
Explore: Life is a journey. I would like to explore the stories behind the data and earn more data analysis skills. I want to explore the advanced programming tools and data visualization softwares to create awesome projects. I want to tell you the interesting stories I discovered in my projects. 
Viz: In the data analysis industry, there are so many branches of subjects, like data mining, statistical computing, data engineering, statistical programming, risk management and etc.. Among all these branches, nothing other than data visualization caught my constant attention. The practice of data visualization is a combination of my artistic side and scientific side. It created a balance for any professionals who are creative but also logical. It made the world of data more beautiful. 
Achieve: The last stage is to achieve our goals. The goal of each project is very unique. I hope my skills can help my future company to achieve their goal and mission. I hope my stories can inspire you to continue pursuing the data visualization. 
Thanks to my professor Jeffrey Shaffer. He taught Data Visualization class at the University of Cincinnati. His inspiring lecture encouraged a lot of students to start their career in data visualization and to invest their time in learning Tableau Software. I would like to invite you to visit his site at www.dataplusscience.com. He provided a lot of Tableau tutorials on his site. 

Tableau Annual Conference 2014

Sep 8 to Sep 12, a huge data party took place in Convention Center in Seattle. It was an amazing week for any data enthusiasts from the data visualization industry. If you miss the conference, just search #data14 on Twitter or Instagram. 

Monday Sep 8
Highlights of the Day: Lunch + Reception 

I had a great lunch with Andy Kriebel, Bryan Brandon, and Alberto Cairo at the Cheesecake Factory just across the street of the Convention Center. It was my first meeting with the members from the Data Viz Team of Facebook
Photo credits for Andy and Bryan. Andy shared his pictures on flickr. Check out here


Reception began in the late afternoon with the warm welcoming music. The giant rectangle screen streamed the live Twitter and Instagram data.. (Yes, we are pretty nerdy :P) 
At the reception, I had a great talk with the data viz professionals. I got to learn that Product Consultant at Tableau was not just a sales person but also a technician for the product. The Product Consultants are responsible for training the employees of Tableau's client companies to learn how to use Tableau in their company, promoting the sales of Tableau software, and generating the visualization for Tableau's client companies. 

And you might be surprised about the quality of food at the reception. They served sushi and yummy Chai Tea Latte. You could get California Rolls, Shrimp Rolls, and fresh Salmon Rolls as much as you wanted. : )

Tuesday Sep 9
Highlights of the Day: Christian Chabot's Keynote Speech + Data Night Out

I attended the fist Keynote by Tableau CEO Christian Chabot. People constantly applauded for the presentation of the new features of Tableau 8.2 Desktop. 

One of the amazing feature is that in the new version of Tableau you can connect the dashboard with a website server by using only 30 lines of Javascript. In a just second, you can finish searching all the constructions in Seattle and visualized it immediately on the dashboard. Another new feature is the story point. Now in one dashboard, you can create more than two pages by adding the story point on the top of the dashboard. Another amazing feature is the Tableau Cloud and the iPad version of Tableau, which gave people the another new option to show the clients the dashboard they made!

Tuesday night is a party night! Tableau reserved the Seattle Center for all the data enthusiasts who registered for the conference. Space Needle, Chihuly Garden and Glass, and EMP museum were free for anyone who came to the party!
(Sorry I did not have many pictures for it..) 


Wednesday Sep 10
Highlights of the Day: Neil deGrasse Tyson's Keynote Speech + Facebook talk + Facebook Party
Keynote on Wednesday was hosted by Neil deGrasse Tyson, whose talk was definitely one of the most funny talk at the conference. He listed some statements from newspaper he collected which included obvious statistical errors :P 


One of the featured talks on Wednesday was Facebook Jeopardy: Hack Edition. Andy and Bryan showed the audience how to grab the data from the server and visualized it on Tableau to study which stickers at Facebook was popular in a month. 

Another interesting featured talk on Wednesday was Porn, Pokemon, and Pop Culture: Using Data That Doesn't Suck. Andy, Jewel, and Peter told their story of Tableau using experience. Jewel's pokemon viz hit thousands of views on Reddit. Another great idea that might inspire fashion designers in NY is Jewel's dress. She collected the music type she listened everyday, generated a viz, and printed the viz on her dress!! A woman sitting in front of me took a picture when Jewel stood out in the front of the stage. 


The Facebook party was a great place for people to share their ideas and thoughts. They delivered nice T-shirts and stickers to people who came to the party. Regardless the party was set up in a bar which you might see in any city, they decorated the atmosphere of the bar with their unique Facebook logo. 


Thursday Sep 11
Highlights of the Day: Iron Viz Championship

My favorite professor at college Jeffrey Shaffer was one of contestants at the Iron Viz Championship. I want to say "Go Bearcat"! 
During the contest, three contestants used the same data of Yelp to create their own viz. You might wonder if Prof. Shaffer's viz is a donut chart but wait.. That's not a donut chart!! You can select a number randomly from the chart so the viz can give you the optional restaurant.. Feeling lucky, right? 

Friday Sep 12 
Friday is the exam day. You can get $100 discounted price for the Tableau exam. But is it something missing? You are right. What will happen next year Tableau Annual Conference 2015? 

SEE YOU IN LAS VEGAS!! 
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Extra

I got a very nice photo from the photo booth at the conference. Tableau streamed my photo on the big screen before the Keynote. I already use the picture as my Linkedin and Twitter profile pictures. 


I would like to end this pose with a picture of sunny Friday afternoon at Fremont as you know sunshine of Seattle, which is famous for rainy days, is very precious. :)