Archive for the ‘Software and Technology’ Category
Assume you have the following table called stories with the following data. And you have run the following query:
SELECT * FROM stories ORDER BY storydate DESC
| id |
source |
title |
storydate |
| 10 |
cnn |
Story 10 |
2010-01-21 |
| 9 |
bbcnews |
Story 9 |
2010-01-20 |
| 8 |
bbcnews |
Story 8 |
2010-01-19 |
| 7 |
skynews |
Story 7 |
2010-01-18 |
| 6 |
cnn |
Story 6 |
2010-01-17 |
| 5 |
bbcnews |
Story 5 |
2010-01-16 |
| 4 |
cnn |
Story 4 |
2010-01-15 |
| 3 |
skynews |
Story 3 |
2010-01-14 |
| 2 |
skynews |
Story 2 |
2010-01-13 |
| 1 |
cnn |
Story 1 |
2010-01-12 |
Now for the challenge. What happens if you are required to get the top two stories from each source? One option is to first get the order of the sources, and then loop through each one of them:
SELECT DISTINCT source FROM stories ORDER BY storydate DESC
<loop “source” as “sourceid”>
SELECT * FROM stories WHERE source = "{sourceid}" ORDER BY storydate DESC LIMIT 2
</loop>
Another option is to do the in MySQL itself! Unsure if there is a better way of doing this, but here’s mine using UNION and Sub Selects:
(SELECT * FROM stories WHERE source =
(SELECT DISTINCT source FROM stories ORDER BY storydate DESC LIMIT 0,1) ORDER BY storydate DESC LIMIT 2)
UNION
(SELECT * FROM stories WHERE source =
(SELECT DISTINCT source FROM stories ORDER BY storydate DESC LIMIT 1,1) ORDER BY storydate DESC LIMIT 2)
UNION
(SELECT * FROM stories WHERE source =
(SELECT DISTINCT source FROM stories ORDER BY storydate DESC LIMIT 2,1) ORDER BY storydate DESC LIMIT 2)
Explanation:
The bold section are subselects and form the WHERE clause of the query. Here we want the first, second and third as per source, but only one at a time. Once we have two results per item, we use UNION to join them together.
One thing to note though. Even though it returns the latest two stories per source, the final table is not sorted by storydate! This can be done using PHP sorting techniques. Is there a way of doing this one time in MySQL?
Fiddler is a useful tool for tracking http requests and responses. It’s similar to the Net tag in Firebug, except that it can be used to track all requests, not only browser-based ones.
For Ubuntu users, the recommended alternative is Wireshark. Wireshark is noted as being more powerful than Fiddler, but the focus will be on the features most commonly used by web developers for tracking.
Installation
Wireshark is found in the Ubuntu repositories, so simply search for wireshark in Synaptic, or enter sudo apt-get install wireshark
Usage
Under Applications > Internet, you will notice there are two options. Wireshark and Wireshark (as root). Run the second one (as root) as this gives you more data to track.
After wireshark has started, the process is straightforward:
- Choose which network interfaces to capture traffic from
- Start capturing
- Filter captured requests
1. Choosing which network interfaces to capture traffic from. From the menu, choose: Capture > Interfaces
This will bring up a list of network devices.
2. Since my work involves debugging work off my laptop (http://localhost etc), I only start device lo (127.0.0.1). This is useful as it immediately ignores all other traffic.
3. The one thing you will notice is that fiddler will log both the TCP and HTTP requests. For the purpose of debugging AJAX, etc., we are only interested in HTTP requests, TCP requests are not required. These can be hidden by adding a filter.
In the field next to Filter:, enter http and click on Apply.
The steps will now show all traffic coming on 127.0.0.1 via HTTP. The last step is picking up the AJAX parts for debugging. Notice that for each request, there is a response. Unlike Fiddler, Wireshark does not combine the request and the response. So click on the response line, and then expand the Line-based text data row. This will show the text of the AJAX response.
Conclusion
Wireshark takes more steps than Fiddler, and Fiddler is a more focussed program than Wireshark. Wireshark also captures traffic without having to install a plugin into firefox, etc., so it’s useful for debugging applications as well. The biggest improvement to make Wireshark truly replace Fiddler is to turn off truncation of the response text. Wish I knew how!
Spotted in Voortrekker Road
For some methods in ExtJS, you will see:
Class Ext.grid.GridDragZone
…
onDrag( Event e ) : void
Abstract method called during the onMouseMove event while dragging an object.
Parameters:
e : Event
the mousemove event
Returns:Class Ext.grid.GridDragZone
void
In this case, GridDragZone is part of GridView which is part of GridPanel. Accessing it will be, GridPanel->GridView->GridDragZone.
The GridDragZone gets implemented for a GridPanel when you set enableDragDrop to true, but it only becomes available when the grid renders, so:
var grid = new Ext.grid.GridPanel({
// etc
});
grid.on('render', function(obj) {
obj.getView().dragZone.onDrag=function(evt){
alert('being dragged');
}
});
Quite a few articles and tutorials show you how to drag and drop a file onto an Adobe AIR application. This one will show you how to drag one FROM an Adobe AIR application TO YOUR DESKTOP (or any other location you provide. The code is really simple:
Drag Me to the Desktop
Download: Source Code
To run, extract files from archive, and then run: adl application.xml
Something that seems to have worked
Thoughts?
Good News for South Africans is that SkypeIn is now available in South Africa! SkypeIn allows users to have the own personal number. People call you from a phone or cell phone and you pick up the call with Skype.
Via MyBroadBand website:
Local Skype users can now get their own SkypeIn number and can make unlimited international calls for R 102 per month
Voice over IP (VoIP) provider Skype recently announced that it has extended its SkypeIn service to South Africa. SkypeIn provides Skype users with their own unique number on which they can receive calls on their computer from regular landline and mobile phone users.
“An online number (SkypeIn) is perfect if you have friends, family or business colleagues who don’t use Skype. Anyone can dial your online number from any phone or mobile and hey presto, your Skype rings and you pick up the call – wherever you are in the world,” the Skype website explains.
“You buy an online number and your friends, family or business contacts can call that number and only pay for a standard rate call (if they are in the same country as your online number) – the online number uses the internet to route the call and so saves them money. It makes absolutely no difference wherever you are, you can pick up the call at no cost to you wherever in the world you are logged into Skype.”
SkypeIn numbers cost US $18 for 3 months or US $60 for a full year. This translates into R 141 for a SkypeIn number for three months and R 471 per number for a 12 month period.
Unlimited International calls for R 102 per month
SkypeIn complements the company’s existing products like SkypeOut and Unlimited flat rated calling. Apart from standard SkypeOut credits, South Africans can purchase South Africa 400, World 400 and Unlimited World packages providing discounted call rates to fixed lines.
South Africa 400, priced at $ 14.95 (R 117), gives subscribers 400 minutes of calls to landlines in South Africa per month. World 400, which costs $ 17.95 (R 141) per month, offers 400 minutes of calls to landlines in South Africa and over 40 countries per month.
The most attractive deal is however the company’s Unlimited World service which at $ 12.95 (R 102) per month allows for unlimited calls to landlines in over 40 countries worldwide. These countries include Australia, France, Germany, Hong Kong, New Zealand, the UK and the United States. Calls to South African landlines are however excluded.
For the past couple of days, I’ve been experimenting with a tool called Focus Booster. It’s a simple app with an easy method to help you measure and increase your focus and concentration:
- Firstly, choose the amount of time you would like to complete a particular task. By default it is set to 25 minutes.
- Prepare to do the task, clear your PC desktop of any distractions, and start the timer.
- Continue working until you’ve completed the task or the timer runs out.
- Take a break
- Restart the process with your next task
Tiny app, simple process, but it works for me, and these are the benefits I believe are derived:
- Forces you to plan and think about a single task you would like to perform
- A quick glance at the timer helps you focus, there is something watching you!
- Helps you to persevere, (just another 8 more minutes to go, etc.)
- Provides some type of measurement of how long you can focus, and challenges you to better it. The next version will allow you to record your focus sessions.
Focus Booster is a free application and requires Adobe AIR to run. Download it at: http://www.focusboosterapp.com/ . Follow updates on twitter @focusboosterapp
There are two ways to uninstall Adobe AIR apps on Ubuntu.
1) Access to original .air file
If you have access to the original .air file, run it and it will give you a screen with options to either Uninstall, Run Now or Cancel. Simply click on Uninstall.
2) Use Synaptic Package Manager
A second more easier approach (particularly if you lost the .air package) is to use Synaptic. From the sidebar, simply choose: Status > Installed (local or obsolete)
Discovering this makes me less hesitant to try our different AIR apps, trying to find out which one works best.
For days now, Thunderbird has been showing one unread email, though I couldn’t find it using all the sort techniques I’ve had. Googling shows it’s not an uncommon occurrence. The solution is also quite easy.
Right click on the folder and choose ‘Compact‘.
Takes a minute, but it will reveal the ‘hidden’ email(s).
Source: https://bugs.launchpad.net/ubuntu/+source/thunderbird/+bug/116642
I'm a Web Developer living in Cape Town, South Africa. Interests include: PHP, JQuery, ExtJS, Adobe AIR, Linux, Ubuntu, WordPress, Human Rights, Usability, Multimedia