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Simple way to transpose columns and rows in SQL?
How do I simply switch columns with rows in SQL?
Is there any simple command to transpose?
9 Answers
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Using arrays or std::vectors in C++, what's the performance gap?
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Now the std::vector vs. native C++ arrays (taken from the internet):
// Comparison of assembly code generated for basic indexing, dereferencing,
// and increment operations on vectors and arrays/pointers.
// Assembly code was generated by gcc 4.1.0 invoked with g++ -O3 -S on a
// x86_64-suse...
Why is creating a Thread said to be expensive?
...e platform specific, but they are not cheap on any Java platform I've ever come across.
A Google search found me an old benchmark that reports a thread creation rate of ~4000 per second on a Sun Java 1.4.1 on a 2002 vintage dual processor Xeon running 2002 vintage Linux. A more modern platform w...
When should I use double instead of decimal?
...nt enough to warrant much thought however.
In all cases, if you want to compare two floating-point numbers that should in theory be equivalent (but were arrived at using different calculations), you need to allow a certain degree of tolerance (how much varies, but is typically very small).
For a...
What's the difference between a Future and a Promise?
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According to this discussion, Promise has finally been called CompletableFuture for inclusion in Java 8, and its javadoc explains:
A Future that may be explicitly completed (setting its value and status), and may be used as a CompletionStage, supporting dependent functions and actio...
Why #define TRUE (1==1) in a C boolean macro instead of simply as 1?
...ch will use the actual boolean type (and resolve to true and false) if the compiler supports it. (specifically, C++)
However, it would be better to check whether C++ is in use (via the __cplusplus macro) and actually use true and false.
In a C compiler, this is equivalent to 0 and 1.
(note that re...
App Inventor 2 字典(Dictionary)操作教程 - 键值对数据结构 · App Inventor 2 中文网
...t", makeDict(pair("phone", "13800138000"), pair("email", "xiaoming@example.com"))), pair("address", makeDict(pair("city", "北京"), pair("district", "海淀区"), pair("street", "中关村大街1号"))))
访问嵌套字典中的值有两种方式：
方式一：逐层获取
global contact = dict...
Are Java static calls more or less expensive than non-static calls?
Is there any performance benefit one way or another? Is it compiler/VM specific? I am using Hotspot.
12 Answers
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Technically, why are processes in Erlang more efficient than OS threads?
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@nilskp: (RE: you comment on point 3…) Even though the language itself has an immutable type system, the underlying implementation — message passing, scheduler, etc. — is a different story altogether. Correct and efficient SMP support di...
Can a C# class inherit attributes from its interface?
...ived class, you need to re-declare the attributes.
If you only care about ComponentModel (not direct reflection), there is a way ([AttributeProvider]) of suggesting attributes from an existing type (to avoid duplication), but it is only valid for property and indexer usage.
As an example:
using S...