Posts Tagged Bug

AVG function returns 0.9999

Posted by smoreau in MySQL on 15 Sep 2011

This one is a very odd bug! 😐

For some reason, the AVG function from MySQL is always returning the value 0.9999 instead of the average value. This has been experienced on MySQL 5.5.12 hosted on Amazon RDS (Relational Database Service).
However, the exact same query executed on MySQL 5.1.28 is returning the right values.

Why is that? Is it a bug in MySQL 5.5.12?
I did a search on internet and I couldn’t find anything about it. So to be honest, I am not sure what is this bug or even if MySQL is aware of it.

Anyway, if you encounter the same problem, you can simply replace the AVG function by the combination SUM/COUNT.
For example, the following query:

SELECT student_name, AVG(test_score)
FROM student
GROUP BY student_name;

can be replaced by the one below:

SELECT student_name, SUM(test_score)/COUNT(test_score)
FROM student
GROUP BY student_name;

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3 Comments

WritableFont doesn’t like to be static!

Posted by smoreau in Java on 18 Jan 2010

While using the tool JExcelAPI within my Java application to generate Excel spreadsheets, I got the following exception:

java.lang.ArrayIndexOutOfBoundsException: 5
	at jxl.biff.IndexMapping.getNewIndex(IndexMapping.java:68)
	at jxl.biff.FormattingRecords.rationalize(FormattingRecords.java:388)
	at jxl.write.biff.WritableWorkbookImpl.rationalize(WritableWorkbookImpl.java:988)
	at jxl.write.biff.WritableWorkbookImpl.write(WritableWorkbookImpl.java:692)
	...

It appears that this exception occurs only when you try to generate more than one Excel spreadsheet! How strange is that! 😯
After a bit of investigation, it seems that the problem comes from the use of the static modifier with a jxl.write.WritableFont variable.

I unfortunately don’t have the time to check the JExcelAPI code source to understand the root cause.
So my advice would be: “if you get EXACTLY the same stack trace, simply delete any static modifier you used with the WritableFont variables”. 🙂

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8 Comments

Onclick event is not fired on IE

Posted by smoreau in Html on 08 Dec 2009

I am pretty sure everybody knows that Internet Explorer has “a few” bugs… 🙄
You didn’t? 😯 Alright, better to stay on your little cloud and leave this blog right away!

For the others, I will talk about the JavaScript event onclick which is not fired when the following requirements are matched:

  • In a form;
  • There is only ONE input text element;
  • There is one button which has an onclick event assigned;
  • You press the ‘Enter’ button inside the input text element.

For a better understanding, let’s now take the following example:

<html>
    <head><title>Test</title><head>
    <body>
        <form>
            <input type="text" id="t1"/>
            <input type="submit" onclick="alert('onclick fired!'); return true;"/>
        </form>
    </body>
</html>

As you can see, there is nothing difficult in this code.
Well, that doesn’t mean Internet Explorer can handle it… 😆

The bug occurs if you press the ‘Enter’ button inside the input text element using Internet Explorer. Indeed, the onclick event is not fired and the text ‘onclick fired!’ is not display to the user! However, it works perfectly fine on Firefox and Safari.

The funny thing is this code works on Internet Explorer if you add another input text, even if it is hidden!
Why? Don’t ask me! 😐

Anyway, the following example works on IE:

<html>
    <head><title>Test</title><head>
    <body>
        <form>
            <input type="text" id="t1"/>
            <input type="text" style="display:none"/>
            <input type="submit" onclick="alert('onclick fired!'); return true;"/>
        </form>
    </body>
</html>

Why are we assigning an onclick event to the submit button?
It could be for a lot of reasons, but the main one is probably to validate the form before submitting the data.

By the way, RichFaces is very often using this event on the submit buttons.
So remember to add a hidden input text to your form if you want to allow users to use the ‘Return’ key. 🙂

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3 Comments