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ALTER TABLE to add a composite primary key
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ALTER TABLE provider ADD PRIMARY KEY(person,place,thing);
If a primary key already exists then you want to do this
ALTER TABLE provider DROP PRIMARY KEY, ADD PRIMARY KEY(person, place, thing);
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STL 算法 - C/C++ - 清泛网 - 专注C/C++及内核技术
...> size_t count(InIt first, InIt last,const T& val, Dist& n);
count_if
<algorithm>
利用输入的操作符,对标志范围内的元素进行操作,返回结果为true的个数
函数原形
template<class InIt, class Pred, class Dist> size_t count_if(InIt first, InIt last, Pred ...
What does Maven do, in theory and in practice? When is it worth to use it? [closed]
...this, it is also the best way to work on a project between people who use different IDEs since IDE-generated Ant scripts are hard to import into other IDEs, but all IDEs nowadays understand and support Maven (IntelliJ, Eclipse, and NetBeans). Even if you don't end up liking Maven, it ends up being t...
Difference between “@id/” and “@+id/” in Android
...efined/created in your project, you use @id/..
More Info
As per your clarifications in the chat, you said you have a problem like this :
If we use android:id="@id/layout_item_id" it doesn't work. Instead @+id/ works so what's the difference here? And that was my original question.
Well, it...
Regex empty string or email
...can't handle it anyway. Try to find a library routine for matching them. If you only want to solve the practical problem of matching an email address (that is, if you want wrong code that happens to (usually) work), use the regular-expressions.info link someone else submitted.
As for the empty st...
Best way to require all files from a directory in ruby?
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There's a subtle gotcha to not stripping the extension. If some other part of the code calls require 'foo' then ruby will load the same file again, which can lead to spurious errors. I added my own answer which explains that and shows how to strip the extension.
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What is the recommended batch size for SqlBulkCopy?
...ts them into a database using SQLBulkCopy. A typical file has about 6M qualified rows, averaging 5 columns of decimal and short text, about 30 bytes per row.
Given this scenario, I found a batch size of 5,000 to be the best compromise of speed and memory consumption. I started with 500 and experim...
java: Class.isInstance vs Class.isAssignableFrom
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Technicality: If obj is null then clazz.isAssignableFrom(obj.getClass()) == clazz.isInstance(obj) will throw a NullPointerException and not return true.
– Andrew Macheret
Apr 23 '18 at 22:14
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What is the correct way to make a custom .NET Exception serializable?
More specifically, when the exception contains custom objects which may or may not themselves be serializable.
7 Answers
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Java switch statement: Constant expression required, but it IS constant
...he sense required by the JLS; see §15.28 Constant Expressions for the specification of a constant expression1. This refers to §4.12.4 Final Variables which defines a "constant variable" as follows:
We call a variable, of primitive type or type String, that is final and initialized with a comp...