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What's wrong with nullable columns in composite primary keys?
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Primary keys are for uniquely identifying rows. This is done by comparing all parts of a key to the input.
Per definition, NULL cannot be part of a successful comparison. Even a comparison to itself (NULL = NULL) will fail. This means a key containing NULL would not work.
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How do I check out a remote Git branch?
Somebody pushed a branch called test with git push origin test to a shared repository. I can see the branch with git branch -r .
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Is it possible to listen to a “style change” event?
Is it possible to create an event listener in jQuery that can be bound to any style changes? For example, if I want to "do" something when an element changes dimensions, or any other changes in the style attribute I could do:
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SQL UPDATE SET one column to be equal to a value in a related table referenced by a different column
I hope that made sense, let me elaborate:
10 Answers
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Use dynamic variable names in JavaScript
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Since ECMA-/Javascript is all about Objects and Contexts (which, are also somekind of Object), every variable is stored in a such called Variable- (or in case of a Function, Activation Object).
So if you create variables like this:
var a = 1,
b = 2,
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Does Swift have access modifiers?
In Objective-C instance data can be public , protected or private . For example:
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Fast permutation -> number -> permutation mapping algorithms
...'s say, 7 elements, 1234567. I know there are 7! = 5040 permutations possible of these 7 elements.
12 Answers
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How to create a file in a directory in java?
If I want to create a file in C:/a/b/test.txt , can I do something like:
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How can I convert a comma-separated string to an array?
...ar array = string.split(',');
MDN reference, mostly helpful for the possibly unexpected behavior of the limit parameter. (Hint: "a,b,c".split(",", 2) comes out to ["a", "b"], not ["a", "b,c"].)
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Find lines from a file which are not present in another file [duplicate]
I have two files (let's say a.txt and b.txt ), both of which has a list of names. I have already run sort on both the files.
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