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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.
Additonally, NULL is al...
How to add http:// if it doesn't exist in the URL?
...hat went on a swim and came back as a fish with the mindset to stop you at all costs from doing and things that might hurt you. There are so many people in the world, and you know, you have this incredible ideas and what you think is missing is motivation, But that is not true. because the way that ...
Cron job every three days
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The answer is not correct because neither suggestion actually runs the job every 3 days. 0 0 */3 * * means run on the 1st, 4th, 7th, etc. (*/3 means 1-31/3 means 1,4,7...31) so the gap will be smaller at the end of the month. (It'll run 2 days in a row if the previous month had 3...
Downloading a picture via urllib and python
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Note for Python 3 it's actually import urllib.request urllib.request.urlretrieve("http://...jpg", "1.jpg"). It's urlretrieve now as of 3.x.
– user1032613
Mar 16 '18 at 0:18
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Maven dependency for Servlet 3.0 API?
...JSTL 1.2, JSF 2.0, JTA 1.1, JSR-45, JSR-250.
But to my knowledge, nothing allows to say that these APIs won't be distributed separately (in java.net repository or somewhere else). For example (ok, it may a particular case), the JSF 2.0 API is available separately (in the java.net repository):
<...
Understanding Apache's access log
...the client IP)
%l is the identity of the user determined by identd (not usually used since not reliable)
%u is the user name determined by HTTP authentication
%t is the time the request was received.
%r is the request line from the client. ("GET / HTTP/1.0")
%>s is the status code sent from the s...
Create singleton using GCD's dispatch_once in Objective-C
...er here: instancetype
+ (instancetype)sharedInstance
{
static dispatch_once_t once;
static id sharedInstance;
dispatch_once(&once, ^
{
sharedInstance = [self new];
});
return sharedInstance;
}
+ (Class*)sharedInstance
{
static dispatch_once_t once;
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How to sort an array by a date property
...e a custom non-enumerable sortBy function using a Schwartzian transform on all arrays :
(function(){
if (typeof Object.defineProperty === 'function'){
try{Object.defineProperty(Array.prototype,'sortBy',{value:sb}); }catch(e){}
}
if (!Array.prototype.sortBy) Array.prototype.sortBy = sb;
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Resharper- Find all unused classes
...g the "Find Usages" option. Is there any way I can see or get the list of all the unused classes or files in my project ?
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How to do parallel programming in Python?
For C++, we can use OpenMP to do parallel programming; however, OpenMP will not work for Python. What should I do if I want to parallel some parts of my python program?
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