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Foreign Key to non-primary key
I have a table which holds data, and one of those rows needs to exist in another table. So, I want a foreign key to maintain referential integrity.
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Why doesn't c++ have &&= or ||= for booleans?
Is there a "very bad thing" that can happen &&= and ||= were used as syntactic sugar for bool foo = foo && bar and bool foo = foo || bar ?
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dplyr summarise: Equivalent of “.drop=FALSE” to keep groups with zero length in output
...ies, levels=c(levels(iris$Species), "empty_level"))
# Species is a factor and empty groups are included in the output
iris %>% group_by(Species, .drop=FALSE) %>% tally
#> Species n
#> 1 setosa 50
#> 2 versicolor 50
#> 3 virginica 50
#> 4 empty_level ...
Updating packages in Emacs
... type package-list-packages, which will take you to the *Packages* buffer (and also update the list of packages), and then type U x.
package-refresh-contents unconditionally tries to download a package list from all repos you've added to package-archives; package-archive-contents is non nil if yo...
Need some clarification about beta/alpha testing on the developer console
The Android developer console has 3 tabs for publishing the app's apk file:
alpha, beta and production, as shown here:
4 An...
Java “Virtual Machine” vs. Python “Interpreter” parlance?
...fined instructions that are supported independent of any specific language and it is generally thought of as a sandbox unto itself. The VM is analogous to an instruction set of a specific CPU and tends to work at a more fundamental level with very basic building blocks of such instructions (or byte ...
Is R's apply family more than syntactic sugar?
...regarding execution time and / or memory.
5 Answers
5
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How dangerous is it to compare floating point values?
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First of all, floating point values are not "random" in their behavior. Exact comparison can and does make sense in plenty of real-world usages. But if you're going to use floating point you need to be aware of how it works. Erring on the side of assuming floating point ...
Browsers' default CSS for HTML elements
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A GitHub repository of all W3C HTML spec and vendor default CSS stylesheets can be found here
1. Default Styles for Firefox
2. Default Styles for Internet Explorer
3. Default Styles for Chrome / Webkit
4. Default Styles for Opera
5. Default Styles for HTML4 (W3...
STL or Qt containers?
What are the pros and cons of using Qt containers ( QMap , QVector , etc.) over their STL equivalent?
14 Answers
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