I'm trying to create a table from another table (CREATE TABLE...AS... statement), but I don't want to insert the rows from the first table. I only need the columns. How?  CREATE TABLE employees24 AS (     SELECT employee_id AS "ID",       first_name,       last_name,       salary,       department_id AS "DEPT_ID"     FROM employees);
I know the statement:  create table xyz_new as select * from xyz;   Which copies the structure and the data, but what if I just want the structure?
I'm trying out  with gnuplot to generate the data.  This works by having pgfplots write some stuff to an external file, run gnuplot on the file, and then use the generated data to plot the graph.  The problem I'm having is that I get different behaviour under xelatex as pdflatex or lualatex.  In xelatex, the data file is littered with ^^I whereas in the other two formats these are tabs.  It appears that the code ^^I is getting stored as a macro which then gets written out to the file, so possibly there's something funny going on with the ^^I syntax: xelatex is reading it literally.  Indeed, when I do \show\pgfplots@TAB (the macro in question) then for pdflatex and lualatex then I get a literal tab whereas for xelatex I get ^^I.  So how do I get a tab in xelatex?  And why isn't \gdef\pgfplots@TAB{^^I} working?  (The previous line in the code, by the way, is \catcode`\^^I=12 - I don't know if that has anything to do with it.) Is my expansion of the state $| x \rangle$ correct? Difference between declaring variables before or in loop? Is there a standard for public key encrypting and signing short messages? Some systems, that operate over flaky bearers, need to send signed, encrypted messages that are entirely self contained - i.e. send a single 300 byte UDP rather than have a 10Kb, two-way, certificate conversation over TCP.  Assume the destination has a private key and already knows the source's public key, and the source has a private key and already knows the destination's public key.  Given this assumption, is there a standard for encrypting/signing a small, but arbitrary length, message?  (I'm well aware of the dangers of rolling my own encryption scheme.)  Would there be a minimum ciphertext size that is related to the public key size?  (I'm thinking plain PKI encryption for plaintexts shorter than the key, and a PKI encrypted AES key for longer plaintexts.) This is homework. I've tried my best to find the best answer that I could understand and could be accepted by my lecturer.   I've searched my lecture notes, wiki and google to find some good explanation defining solar irradiance. But somehow I still don't understand how I should 'define solar irradiance'. Can someone give me a few good sentences explaining solar irradiance. What are the changes, if any, in a photovoltaic cell (in terms of short-circuit current and open-circuit voltage) if the irradiance is reduced by 50%? OK...before everyone blasts this with references to the relativistic invariance of the physical laws, time dilation, etc let me add some context. Also, I am an amateur with an interest in physics, so I don't know the details of the physics. However, I have read enough about the cosmological principle and cosmic time to develop this "confusion" .  Based on evidence gathered to-date, it appears that the universe is both , as evidenced by observations and the . This principle, when combined with the FLRW metric, allows space-time to be divided into non-intersecting slices and therefore establish a "cosmic time."   Now, the existance of such a time in no way suggests that it is the "right" time or a true "now", hence violating relativity -- although some presentist philosophers (e.g., W.L. Craig) have tried to make this argument, but it is not generally accepted in philosophical circles.  However, this leaves me confused about an apparent disconnect between relativity and the cosmological principle:  Isotropy only holds if we are at rest relative to the cosmic microwave background radiation (universal rest frame), o/w anisotropy is present - yet each reference frame is supposed to allow equally valid observations. How can these two be reconciled when most reference frames would lead us to conclude that the universe is NOT isotropic?  It seems that only by appealing to the idea of being at rest relative to "universal rest frame" can we explain away any discrepancies from isotropy as due to "peculiar motion". However, doesn't this give this "universal rest frame" and its associated time an empirically privileged status, even though physical laws work just fine in every reference frame?   For example (pardon any abuse of astronomy): if look off in some part of space and see only quasars, and then in another part of space and see only brown dwarfs, but I measure both as apparently the same distance from me, then can I conclude that we are in motion, since otherwise we would have an empirical contradiction (kind of like finding dinosaur and human remains in the same strata)?  Any help on where I am going wrong would be helpful. Intuitively, I don't think there should be a way to establish absolute ordering between space-like separated events, but the above reasoning suggests otherwise. How to find the smallest $n$ such that $n^a\equiv 1 \pmod p$ Why does do-release-upgrade on Xubuntu running version 18.04 not offer to update to 20.04.1? I've understood that when I run the Software Updater GUI program, or when I execute do-release-upgrade on the command line, it should offer to upgrade to the latest LTS release if (1) I've got the release update behaviour set to lts, and (2) if the first point release of a newer LTS release is available. I have a couple of machines running the Xubuntu LTS release 18.04. The contents of file etc/update-manager/release-upgrades on all these machines is [DEFAULT] Prompt=lts  That satisfies condition (1). Also, it seems that Xubuntu 20.04.1 is already released, satisfying condition (2). However, neither do-release-upgrade nor the Software Updater offers to upgrade to that release. Why? Edited to add: It seems this question is a duplicate of . What is the term for taking it out on someone even though you will be harmed by this too? When you are so mad at someone that you make a bad decision, even though you will be harmed by it as well, in order to harm that person; is there a good term for this?   For example burning $100 because he owns $20 of it. Uninstalling Ubuntu from dual boot / changing bootloader Hyperlinks to web sites using anchors sometimes don't work Standard value of PATH variable Windows 10 After having poorly handled the PATH system variable (resulting in deletion), I'm now looking to reinstate the variable with the original value. I found answers like  about Windows 8 and below, but not for Windows 10. I guess values are virtually identical, but I'd like to know the exact string so I'm not missing anything. EDIT: Also, Regedit tree have changed and I'm not able to locate the variable How can I prove that $\gcd(a, b) = \gcd (a, b + ma)$?  I have tried this:  let $g = \gcd(a, b)$, then $g \mid a$ and $g \mid b$. This means that $g \mid ax+by$.  I don't know what to do next.  Thanks. Remove files with 0 length inside bash I want to create a bash script inside Linux terminal to go into a file and then delete it if it's empty:  #!/bin/bash echo " Enter name of a directory" read Dir for Directory in $( ls $HOME ) do    test -d $HOME/$dir   if [ $# -eq 0 ]   then      for filename in $( ls $HOME/$Dir )     do        test -d $HOME/$dir/$filename       if [ ! -s "$filename"  ]       then         rm $HOME/$dir/$filename       else          echo " not empty"       fi      done    else      echo " $Dir is not a directory"    fi  done   This is the code I am using but it does not work. It recognizes the file created but doesn't delete it even when empty. It Salah displays there is no such file or directory I have a Linux CentOS server, the OS+packages used around 5GB. Then, I transferred 97GB data from a Windows server to two folders on this Linux server, after calculated the disk usage, I see the total size of the two folders is larger than the disk used size.  Run du -sh on each folder, one use 50GB, the other one use 47GB  But run df -h, the used space is 96GB. (50GB + 47GB + 5GB) > 96GB  Is there any problem? Those two folders contain lots of files (1 million+). Thanks. Let us have a surface $X$ which satisfy the equation $\omega^3 = (z-1)(z-2)\cdots (z-8)$ It's stated in the task, that there are exactly $g$ holomorphic differentials on the curve. How can I find $g$ and construct them?  The genus $g$ of this curve (I tried to use Riemann-Hurwitz theorem)  The map $X(z,\omega) \to CP^1(\omega)$ has degree 3. and we have 8 branching points with 3 leaves at each. $\chi(Domain) = DegreeOfMap * \chi(Target) - \sum_{points}(BranchingLeaves - 1) $ $2-2g = 3 *(2) - 8*2 $ hence $ 12 = 2g$ and  $g = 6$ I know that in case of hyperelliptic curve there are $g-2$ (If i'm not mistaken) holomorphic differetials and they are of sort $\frac{z^k dz}{w}$. But the form of the curve equation was heavily used. UPD: there is a branhing point at $\infty$, because if we go around all points $ 1 \cdots 8$ at once, we get that cubic root of the right side is multiplied by $\exp{4 \pi /3}$ $2-2g = 3 *(2) - 9*2 $ hence $ 12 = 2g$ and  $g = 7$ (I hope that this is true) I have the message:   Error Broken count &gt;0 Check if you are using third party repositories. If so disable them, since they are a common source of problems. Furthermore run the following command in a Terminal: apt-get install -f Details: The following packages have unmet dependencies: firefox-globalmenu: Depends: firefox (= 19.0+build1-0ubuntu0.12.04.2) but 19.0+build1-0ubuntu0.12.04.1 is installed   Any suggestions? Why is asking a question on "best practice" a bad thing? I want to show that for each $n \in \mathbb N$ it holds that $$\sum_{k = 0}^\infty \frac{n^k}{k!} \vert k - n \vert = 2n \frac{n^n}{n!}.$$ But I have absolutely no idea how to do that. I tried to split the series like this:  $$\sum_{k = 0}^\infty \frac{n^k}{k!} \vert k - n \vert = \sum_{k = 0}^{n - 1} \frac{n^k}{k!}(n - k) + \sum_{k = n + 1}^\infty \frac{n^k}{k!} (k - n)$$ Now I want to show that $\sum_{k = 0}^{n - 1} \frac{n^k}{k!}(n - k) = \sum_{k = n + 1}^\infty \frac{n^k}{k!} (k - n) = n \frac{n^n}{n!}$ holds. But I got no idea how to achieve that. I tried to use induction but things became pretty messy and I don't think it will work like that. On the other hand I got the idea that it might have to do with $\exp$ or binomial coefficients but I don't see where I can facilitate that. I would appreciate some hints :) What effect does serial downvoting have on my rep cap? So I was the victim of serial downvoting the other day, and just had it automagically reversed. Rather than simply removing the previous votes, I was given a bonus lump of rep with the reason "serial downvote reversal". The downvotes and the bonus show up on different days. Since a whole day's quota worth of downvotes equates to quite a fraction of my daily rep cap, what happens in the following circumstances?   I get 200+ rep on a particular day, but I am serial downvoted (later reversed) back to under 200. Does this day count as reaching cap? I get 200+ rep the next day, and I am also credited back the rep. Is the rep bonus immune to the rep cap in the same way bounties are? On the day I get my rep bonus, it is enough to take me to 200 rep. Does this count as capping?