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difference between primary key and unique key
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Primary Key:
There can only be one primary key in a table
In some DBMS it cannot be NULL - e.g. MySQL adds NOT NULL
Primary Key is a unique key identifier of the record
Unique Key:
Can be more than one unique key in one table
Unique key can have NULL values
It can be a candidate key
Unique k...
How do you write multiline strings in Go?
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According to the language specification you can use a raw string literal, where the string is delimited by backticks instead of double quotes.
`line 1
line 2
line 3`
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Where is virtualenvwrapper.sh after pip install?
...e, pointing towards virtualenvwrapper.sh. I've checked all the python and site-packages directories, and I can't find any virtualenvwrapper.sh. Is this something I need to download separately? Is pip not installing correctly?
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super() in Java
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super() calls the parent constructor with no arguments.
It can be used also with arguments. I.e. super(argument1) and it will call the constructor that accepts 1 parameter of the type of argument1 (if exists).
Also it can be used to call methods from the parent...
What is Unicode, UTF-8, UTF-16?
... or UTF-16?
I have researched this on Google and searched here as well but it's not clear to me.
9 Answers
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Why should I prefer single 'await Task.WhenAll' over multiple awaits?
...task completion and just need them all to complete, should I still use await Task.WhenAll instead of multiple await ? e.g, is DoWork2 below a preferred method to DoWork1 (and why?):
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Calling Objective-C method from C++ member function?
... have a class ( EAGLView ) which calls a member function of a C++ class without problems. Now, the problem is that I need to call in that C++ class a objective-C function [context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer*)self.layer]; which I cannot do in C++ syntax....
Combining C++ and C - how does #ifdef __cplusplus work?
...m working on a project that has a lot of legacy C code. We've started writing in C++, with the intent to eventually convert the legacy code, as well. I'm a little confused about how the C and C++ interact. I understand that by wrapping the C code with extern "C" the C++ compiler will not ...
Swapping two variable value without using third variable
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Using the xor swap algorithm
void xorSwap (int* x, int* y) {
if (x != y) { //ensure that memory locations are different
*x ^= *y;
*y ^= *x;
*x ^= *y;
}
}
Why the test?
The test is to ensure that x and y have diffe...
How to do a logical OR operation in shell scripting
I am trying to do a simple condition check, but it doesn't seem to work.
8 Answers
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