大约有 15,000 项符合查询结果（耗时：0.0296秒） [XML]
CROSS JOIN vs INNER JOIN in SQL
...ults, Innerjoin will only return 100 rows in the same situation.
These 2 examples will return the same result:
Cross join
select * from table1 cross join table2 where table1.id = table2.fk_id
Inner join
select * from table1 join table2 on table1.id = table2.fk_id
Use the last method
...
Is there a performance gain in using single quotes vs double quotes in ruby?
...
$ ruby -v
ruby 1.9.3p0 (2011-10-30 revision 33570) [x86_64-darwin11.0.0]
$ cat benchmark_quotes.rb
# As of Ruby 1.9 Benchmark must be required
require 'benchmark'
n = 1000000
Benchmark.bm(15) do |x|
x.report("assign single") { n.times do; c = 'a string'; end}
x.report("a...
Removing X-Powered-By
...
I think that is controlled by the expose_php setting in PHP.ini:
expose_php = off
Decides whether PHP may expose the fact that it is installed on the server (e.g. by adding its signature to the Web server header). It is no security threat in any way, but...
How to “test” NoneType in python?
... I question a variable that is a NoneType? I need to use if method, for example
7 Answers
...
Generate random password string with requirements in javascript
...
Forcing a fixed number of characters is a bad idea. It doesn't improve the quality of the password. Worse, it reduces the number of possible passwords, so that hacking by bruteforcing becomes easier.
To generate a random word consisting...
Applicatives compose, monads don't
... values. This really bites. Compare
miffy :: Monad m => m Bool -> m x -> m x -> m x
miffy mb mt mf = do
b <- mb
if b then mt else mf
which uses the result of some effect to decide between two computations (e.g. launching missiles and signing an armistice), whereas
iffy :: Appl...
What is the rationale for all comparisons returning false for IEEE754 NaN values?
... are not real numbers, and floating-point arithmetic does not satisfy the axioms of real arithmetic. Trichotomy is not the only property of real arithmetic that does not hold for floats, nor even the most important. For example:
Addition is not associative.
The distributive law does not hold.
Th...
What's the difference between std::move and std::forward
... with "t" being template param is special, and adjusts "t" to be
(for example) "int &" or non-ref "int" so std::forward knows what to do. */
void forwarding( t && arg ) {
std::cout << "via std::forward: ";
overloaded( std::forward< t >( arg ) );
std::cout <...
Why do people say there is modulo bias when using a random number generator?
...am going to post one here which will hopefully help people understand why exactly there is "modulo bias" when using a random number generator, like rand() in C++.
...
Intelligent point label placement in R
...oblem:
I did this by hand in Preview (very basic PDF/image viewer on OS X) in just a few minutes. (Edit: The workflow was exactly what you'd expect: I saved the plot as a PDF from R, opened it in Preview and created textboxes with the desired labels (9pt Helvetica) and then just dragged them arou...