I'm puzzled by this in Oracle  select case when 'hello' &lt;&gt; '' then 1 else 2 end from dual;   returns 2  select case when 'hello' &lt;&gt; 'hello' then 1 else 2 end from dual;   returns 2  however on SQL*Server this works as expected.
I know that it does consider ' ' as NULL, but that doesn't do much to tell me why this is the case.  As I understand the SQL specifications, ' ' is not the same as NULL -- one is a valid datum, and the other is indicating the absence of that same information.  Feel free to speculate, but please indicate if that's the case.  If there's anyone from Oracle who can comment on it, that'd be fantastic!
I'm trying to prove whether or not the Laurent polynomials $\mathbb{Z}[x, x^{-1}]$ with coefficients in $\mathbb{Z}$ form a principal ideal domain.    I know that $\mathbb{F}[x, x^{-1}]$ is a PID when $\mathbb{F}$ is a field, but clearly $\mathbb{Z}$ is not a field so I cannot appeal to this result. And my intuitions are not serving me very well at the moment. Can anyone provide a hint or direction to take? Is there a single word to describe a solution that hasn't been optimized? I am working with some code, and I would like to describe the difference in its performance when it is optimized versus when it is not optimized. Unfortunately, I can't find a word to describe the code before it is optimized; "sub-optimal" might work, but I want to emphasize that this is the first iteration of the code. If "unoptimized" were a word, I would use that, but I haven't found any references to it in any dictionary.  Perhaps "raw" or "original"? I have installed the pimd service by means of apt. This comes with an upstream systemd unit file (/lib/systemd/system/pimd.service).  I want the service to be restarted when for some reason it gets killed, hence I wish to add the line Restart = always in the unit file.   However, I don’t want to modify the upstream unit file.  Is there any workaround for this? Add Point to Plot3D Let $q \in \mathbb C$, $|q|=1$ and $q^n \neq 1, \forall n \in \mathbb N$. Show that $\{q^n:  n \in \mathbb N\}$ is dense in $S^1$.  My attempt: As $(q^n)$ is limited, there is subsequence $(q^{n_j})$ convergent. So given $\epsilon &gt; 0, \exists j_0 \in \mathbb N, \quad |q^{n_j} - q^{n_k}| &lt; \epsilon, \quad \forall j,k \geq j_0$. Supose that $n_j &gt; n_k$, then  $|q^{n_j} - q^{n_k}| = |q^{n_k}||q^{n_j - n_k} - 1| = |q^{n_j - n_k} - 1| &lt; \epsilon, \quad \forall j, k \geq j_0$. So, there is a subsequence of $(q^n)$ that converges to $1$.  Using this fact, how can I ensure that for all $w \in S^1$ there is a subsequence of $(q^n)$ that converges to  $w$? Mortarboard badge not awarded Extend a language with additional keywords? I have been using LaTeX for a long time now, and I find myself often going to this website to solve my problems. This often includes copy pasting codes which include \newcommand, \newenvironment and \def. I think it is time I start to learn how to use them so I can solve my problems myself! It is always better if you actually know what is going on inside your code.  I am wondering if there is any turtorial or book out there that handles how to use those commands. Or is the best way to learn to just mess with a random file?   Thanks in advance!  (Also this is my first time I post here after using this website for so long, I really appreciate everyone who posts and tries to help other people here!) Standard packages for compact SMT crystals There is an old and bog standard form factor for SMT crystals - HC49/US. The problem is that HC49/US takes a lot of real estate on the board.  It's 12mm long.  Another problem with crystals and oscillators in general is that they often become long lead time items.  [This is my experience.]  There are lots of small form factor crystals from various manufacturers.  But, at a glance, it seems that there is no standardization of form factor.  It’s nice when packages are standardized.  It alleviates the long lead time problem.  Crystals from manufacturer B may be used, if crystals from manufacturer A are out of stock.  Are there standard form factors for compact SMT crystals?  Update  Armed with the insights from Gribo and Gustavo, I did a more focused survey.  Found that 12MHz in 3.2x2.5mm package are produced by: Abracon, Citizen, Epson, Fox, ECS, TCS, NDK.  To be included in this list, the part had to be in stock at DigiKey.  It turns out that 3.2x2.5mm package is common across many manufacturers. Exclude TeX.SE question titles from MathJax parsing in Hot Network Questions Recently, the TeX.SE question  got onto the Hot Network Questions list.  Like many questions on TeX.SE, it contains some TeX markup in its title.  Unfortunately, on , this markup gets parsed and rendered as math:    I propose that either:   the entire Hot Network Questions sidebar should be excluded from MathJax parsing by styling it with the tex2jax_ignore class, or at least, any hot questions from TeX.SE should be so excluded from MathJax parsing.   Or I suppose we could always implement , which asks for all questions with TeX in the title to be excluded from Hot Network Questions entirely.  That might be throwing out the baby with the bathwater, though.    Ps. This issue is partially masked by , which causes MathJax not to be rendered in many elements that are hidden by default and revealed using jQuery .show(), such as all but the first five questions in the Hot Network Questions sidebar.  The  user script contains a generic fix for that bug, so users who have it installed will see this issue more frequently, but it occurs even without SOUP whenever a question with TeX markup in the title happens to show up among the top five hot questions that are always visible by default. I have, not one but two microSD cards that my phone (Samsung Galaxy Young, Gingerbread OS) seem to have broken. One is 1GB and the other is 2GB. The 1GB one won't be formatted.  When I put the 1GB one into the computer the computer prompts for a formatting. I don't care for the content so I tried to format it, but to no avail; the format fails and I have no idea what to do to make it work again.  I tried using the SDformatter software, but it can't format the card as it is write protected. I'm googling to solve it but so far no success.  My computer OS is win7 if that's of any relevance. Altium - create a mirror image of a board I want to create an identical motor drive board in the right and left sides.  I just finished layout for the right side and I am wondering what is the easiest way to create the mirror image of this board for the left side?  For example: the connectors on the "top" side would now be on the bottom of the other board.  All components and tracks will also switch sides, layer stack will be inverted, etc.  Is there any command sequence in Altium that will do this without me having to manually re-assign everything to the other layer? For some reasons, I would like to do an explicit quoting of a string value (becoming a part of constructed SQL query) instead of waiting for implicit quotation performed by cursor.execute method on contents of its second parameter.  By "implicit quotation" I mean:  value = "Unsafe string" query = "SELECT * FROM some_table WHERE some_char_field = %s;" cursor.execute( query, (value,) ) # value will be correctly quoted   I would prefer something like that:  value = "Unsafe string" query = "SELECT * FROM some_table WHERE some_char_field = %s;" % \     READY_TO_USE_QUOTING_FUNCTION(value) cursor.execute( query ) # value will be correctly quoted, too   Is such low level READY_TO_USE_QUOTING_FUNCTION expected by Python DB API specification (I couldn't find such functionality in  document). If not, maybe Psycopg2 provides such function? If not, maybe Django provides such function? I would prefer not to write such function myself... Why is a linear transformation called linear? Making an Emission shader emit a different colour of light than the colour assigned to the object? Unable to modify files/folders in NTFS partition Is there a good way to determine the value of magic items in 5e? In 5e, magic items aren't as common or as varied as in older editions, but that also means it is hard to place prices on them.  As DM, NPC's can't really sell a magic item because we don't know the prices for these items. While it is stated that they are rare and usually unpurchasable and unsellable, but I still have to have some basis on what to price them.  So is there a way to find buying and selling prices for magic items in 5e? What exactly do quotation marks around the table name do? I thought that the quotation mark (") was simply a type of grouping marker but I'm debugging some NHibernate code and notice that while  SELECT * FROM site WHERE site_id = 3;   Works fine  SELECT * FROM "site" WHERE site_id = 3;   fails with a table or view does not exist error.  What gives? I just installed Ubuntu 16.10 on my desktop and have a USB deathadder. The problem is I can't see where the cursor actually is because it appears only in the top left of my screen. The mouse still moves but the cursor graphic doesn't follow How to connect to Salesforce REST API without OAuth? How does Jitterbit do it?