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Can a foreign key be NULL and/or duplicate?
...at field must exist first in a different table (the parent table). That is all an FK is by definition. Null by definition is not a value. Null means that we do not yet know what the value is.
Let me give you a real life example. Suppose you have a database that stores sales proposals. Suppose furth...
Proper way to rename solution (and directories) in Visual Studio
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Manually edit .sln file
This method is entirely aimed at renaming the directory for the project, as viewed in Windows Explorer.
This method does not suffer from the problems in the Remove/add project file method below (referenc...
Can I restore deleted files (undo a `git clean -fdx`)?
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No. Those files are gone.
(Just checked on Linux: git clean calls unlink(), and does not backup up anything beforehand.)
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how to install gcc on windows 7 machine?
I have MinGW on my windows 7 machine. I wish to install and use complete gcc for C compiler. I found there is no single pre-compiled ready-made installation file for this purpose. I checked the following page : http://gcc.gnu.org/install/
It is difficult and I find it above my level of understandi...
HTTP vs HTTPS performance
...any major differences in performance between http and https? I seem to recall reading that HTTPS can be a fifth as fast as HTTP. Is this valid with the current generation webservers/browsers? If so, are there any whitepapers to support it?
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INNER JOIN vs LEFT JOIN performance in SQL Server
... slower; by definition, an outer join (LEFT JOIN or RIGHT JOIN) has to do all the work of an INNER JOIN plus the extra work of null-extending the results. It would also be expected to return more rows, further increasing the total execution time simply due to the larger size of the result set.
(A...
Ruby off the rails
... the huge benefits of Ruby is the ability to create DSLs very easily. Ruby allows you to create "business rules" in a natural language way that is usually easy enough for a business analyst to use. Many Ruby apps outside of web development exist for this purpose.
I highly recommend Googling "ruby ...
What do two question marks together mean in C#?
...e following statement will assign the first non-null Answer# to Answer (if all Answers are null then the Answer is null):
string Answer = Answer1 ?? Answer2 ?? Answer3 ?? Answer4;
Also it's worth mentioning while the expansion above is conceptually equivalent, the result of each expression is o...
How to show the last queries executed on MySQL?
Is there any query/way to show the last queries executed on ALL servers?
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Is it possible to read the value of a annotation in java?
...ation and if the annotation policy retains the annotation at runtime. Naturally if the retention policy doesn't keep the annotation at runtime, you won't be able to query it at runtime.
An answer that's since been deleted (?) provided a useful link to an annotations tutorial that you may find helpf...