SQL multiple column unique
How do I specify unique constraint for multiple columns in MySQL?
How to remove Ubuntu and put Windows back on? Canonical has recently announced , which is Ubuntu with a specific interface for mobile devices.  Where can I get phones with this version of Ubuntu pre-installed? If no devices are available yet, where can I pre-order one? How can I remove a commit on GitHub? There exist several implementations of the GBDT family of model such as:   GBM XGBoost LightGBM Catboost.    What are the mathematical differences between these different implementations?  Catboost seems to outperform the other implementations even by using only its default parameters according to , but it is still very slow.  My guess is that catboost doesn't use the dummified variables, so the weight given to each (categorical) variable is more balanced compared to the other implementations, so the high-cardinality variables don't have more weight than the others. It allows the weak categorical (with low cardinality) to enter to some trees, hence better performance. Other than that, I have no further explanation. The sentence     Women driving cars is, of course, such a foreign sight to a society like   Saudi Arabia   The subject is not "women" (otherwise, the verb would have been 'are'); the subject, as I mean to use it, is the rarity of seeing women driving cars. The subject, in other words, is "women driving cars" as a thing. Does this give me licence to use 'is' here? Thank you. Is it correct to say "What was your name?"? The reason I am asking this is, generally the name of the person will not change. One should say "What is your name?" Why is the Converse to Lagrange's Theorem False? How to create a Facebook page without a personal account In the past, Facebook used to let business create pages or apps without a personal account. This account created in the page/app creation process had limited capacities and could be switch to a full personal account after—if needed (irreversible).  But today, if I want to create a page for a new brand, without having a Facebook account, it seems I can’t anymore. And I can’t find any communication from Facebook regarding this change.   Anybody has any info? Is it still possible (in a new way maybe)? How can I increase the mouse pointer speed beyond the limits set by the Mouse preferences dialog? In the Mouse preferences dialog I've set the acceleration to max and the sensitivity to min and the mouse pointer is not exactly sluggish, but I'd like to make it even faster. Is it possible to be done by setting some value in the procfs or something?  Thanks! Let $p$ be a prime number, and let $\mathbb{F}_p$ be the field with $p$ elements. How many elements of $\mathbb{F}_p$ have cube roots in $\mathbb{F}_p$?   I had this question on an exam and after reviewing I am still not sure. Any help would be appreciated. What is a terminal and how do I open and use it? Smart Phone's camera socket Version Control: Entire site or just pieces? I've been using git to track changes in the plugins and themes I've developed for different sites. Each plugin or theme has their own repository in whichever local install of WordPress I happen to be using for that project. This works fine when I'm just working on one solitary plugin or theme.  But when I have a local version of an entire site which is a collection of different plugins, themes, WordPress core, etc. Should I be keeping that entire directory under version control?  Is there a best practice to always have a collection of repositories for each theme/plugin, or for each client site to have one monolithic repository that includes all the code used in the project (including the latest copy of WordPress via svn.) Is it possible to use multiple here-docs in bash? Can one use multiple here-docs to provide input to a command in bash?  $ cat &lt;&lt;&lt;foo &lt;&lt;&lt;bar bar $ cat &lt;&lt;EOF1 &lt;&lt;EOF2 &gt; foo &gt; EOF1 &gt; bar &gt; EOF2 bar   Obviously, in both cases, the second here-doc is used as stdin, and replaces the first reference. Is the solution to use echos instead?  $ cat &lt;(echo -n foo) &lt;(echo bar) foobar   Also, for some reason, using a combination didn't work for me. Why would that be?  $ cat &lt;&lt;&lt;foo &lt;(echo bar) bar $ cat &lt;(echo -n foo) &lt;&lt;&lt;bar foo How to connect to my web server? What is the source for defaulting to plain English readings of non-game terms? Send authors an inbox message if their question is closed I am given the information that $ \vec{u} = \langle 1, 1/2 \rangle$ and $\vec{v} = \langle 2,3 \rangle$.   There are a few pieces I am asked to find, and these are the one I am having trouble with:   $\left\Vert \large \frac{\vec{u}}{|| \vec{u}||}\right\Vert$  The magnitude of vector u is $ \sqrt{5}/2$, of which I correctly calculated; the unit vector is then $ \langle \large \frac{2 \sqrt{5}}{5}, \frac{ \sqrt{5}}{5} \rangle$. However, when I go to find the magnitude of the unit vector, I get $ \sqrt \frac{3}{5}$, which is clearly not one. What did I do wrong? In which way does quantum mechanics disprove determinism? Is there a constraint that restricts my generic method to numeric types?