Better performance to have nullable columns or an extra table?
Why shouldn't we allow NULLs?
How to identify the process locking a file? Better Information On Defense Damage Clash of Clans The way that Clash of Clans chooses to convey information about how much damage defense buildings output is bad. The current method of telling the user that a mortar does X dmg a second is pretty worthless since they fire much slower than once a second.  Where can I find a break down / what is the damage break down for how much damage these buildings do per shot rather than per second?  Sure, information on each level of the buildings would be nice but if that is too much I think simply providing the data for level one of each building would also work. I want to prove that $\lim_{(x,y)\to (0,0)} \frac{\sin(x+y)}{x+y} = 1$  Is it sufficient to say that if $u = x+y$ then as $(x,y) \rightarrow (0,0)$ then $u \rightarrow 0$ and then evaluate $\lim_{u\to 0} \frac{\sin u}{u}$ which is 1 by L'Hôpital's rule?  I feel that this is somehow "cheating" and I would really like to prove it in a more rigorous way, i.e., by using an $\epsilon$ - $\delta$ argument.  I have tried for a long time to use the one variable version and prove that if $0 \lt \sqrt{x^2 + y^2} \lt \delta$ then somehow $0 \lt |x+y| \lt \delta$ and it would follow from the one variable case that $| \frac{\sin(x+y)}{x+y} - 1| \lt \epsilon$. However, because $|x+y| = 0$ when $y = -x$ I am not getting anywhere with this.  Any input on this would be helpful :) Where do I find system sounds? After installing gm-notify I see the option of hearing a sound every time a new e-mail arrives in my Gmail inbox, but I don't know where Ubuntu (10.4) stores the system sounds to assign one. Any ideas? Thanks. How is voltage always able to increase, if electrons move at the speed of light? I want my Qt application to be able to save simple vector graphics to clipboard in a compatible way. On windows I want to be able to paste the graphics into Microsoft Word or Powerpoint. On Linux I want to be compatible with the Open Office.   Which format would you recommend? Can Qt generate EMF in an easy way? Is SVG an option?  Update:  My current plan is to add a piece of native win32 code to render the graphics to emf on windows. This code will not be available on linux. How to use the  method?  Say I want to find number of combinations I can get with $x_1+x_2+x_3+x_4=22$,  where $x_i\in\mathbb{N}$.  Is this the correct time to apply the method?  This is being repurposed in an effort to cut down on duplicates, see here:     and here: Lubuntu Installer Giving Error after Partition creation "YOUR SYSTEM MAY OR MAY NOT BOOT " I was replacing my Ubuntu 18.04 with Lubuntu 20.04. I wanted to keep my /home partition same. After creating /root , swap and changing mount point for /home partition the installer gave a warning that /boot/efi partition is not created Lubuntu 20.04 needs /boot/efi partition to boot. Please create a FAT32 partition and mount it as /boot/efi and enable flag esp. Then I created the /boot/efi  partition but there was no esp flag(s). I had installed Ubuntu 18.04 alongside windows10. What should I do now? How do I make an object face the mouse position, but only on one plane? What is a good asymptotic for $f_n = f_{n-1}+\ln(f_{n-1})$? I have a pretty simple table that needs to span multiple pages. This seems like a job for either the / package or the  package.   The voting on the answers to this  suggest that longtable is the preferred package, yet xtab is much newer and has been revised since that question was asked.  What are the differences between xtab and longtable and when is one preferable to the other? I got pretty confused at that question... Can anyone help me understand this question better and/or drop some hints please? Thank you! help you learn vs. help you to learn Source:  by Douglas Crockford (2008) Example:  My goal here is to help you to learn to think in JavaScript. I will show you the components of the language and start you on the process of discovering the ways those components can be put together.  Although it is usually the case that you mostly hear people say something like &quot;this will help you become a better person&quot;, is there any particular reason as to why he chose not to leave out the to and say help you to learn instead? If you've got something interesting to say, could you please elaborate on it as well? I would very much like to receive some coherent explanation and get this thing finally straight. The only time I know of, though, that you would use the to is when you say it like this:  It helps a lot to think of the rather difficult concept of classes used in modern software development as mere blueprints that architects and builders use to build houses. In life, it really helps to know your times tables by heart because not all the time do you have a calculator on you.  Because the aspect of the verb &quot;help&quot; is a little bit different here. But in all other cases, help do or help you do something is by far more common. How are connections differentiated from behind NAT routers? I'm trying to model my face on Blender using  and it gives links to reference photos.  The thing is, as I mentioned above, I want to try and model my face.  So I've decided to take photos of my face. But it doesn't seem to be working well (not symmetrical enough and stuff), so how exactly should I take my reference photos so that it would work well when I try to model it with the Mirror modifier?  Note: I only have the 'webcam' on my Macbook Pro and the camera on my Hongmi phone and I don't want to spend money on a new camera. How to prove that the number $1!+2!+3!+...+n!$ is never square? Most useful additions in KOMA-Script? (Background: I'm a beginner who will mostly use LaTeX for university articles and reports, but no math. Also, as I reside in Canada, the German typography conventions, which I understand KOMA-Script supports better than LaTeX, are less relevant).  I've read that the KOMA-Script package has a lot of improvements for the default document classes. Yet the 's length, about 250 pages, is somewhat daunting. I plan to read the chapters I'm interested in anyway but it'd be useful to have some pointers about low hanging fruits. I searched the site and  answers say KOMA-Script adds improvements but do not delve into details.  I'll ask this as a community wiki topic and, since the audience of this site is international, feel free to mention German typography if KOMA-Script is better there. Should I use the past tense with did? For example, I was to say:     The important question is: Did they knew what it means or not?   Or should I say:     The important question is: Did they know what it means or not?   In other words: Should I use past tense with did?  I looked at this:    but it didn't really answer my question. Make Vim show ALL white spaces as a character How do I remove/delete a folder that is not empty? I am getting an 'access is denied' error when I attempt to delete a folder that is not empty. I used the following command in my attempt: os.remove("/folder_name").   What is the most effective way of removing/deleting a folder/directory that is not empty?