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Unique constraint that allows empty values in MySQL
...traint such that all values in the index must be distinct. An error occurs if you try to add a new row with a key value that matches an existing row. For all engines, a UNIQUE index allows multiple NULL values for columns that can contain NULL.
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HTML Script tag: type or language (or omit both)?
... following error:
Line 4, Column 41: required attribute "type" not specified
So if you're a fan of standards, use it. It should have no practical effect, but, when in doubt, may as well go by the spec.
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JUnit confusion: use 'extends TestCase' or '@Test'?
...MyException e) {
// ok!
// check for properties of exception here, if desired
}
}
JUnit 5 introduced yet another API change, but still uses annotations. The new @Test annotation is org.junit.jupiter.api.Test (the "old" JUnit 4 one was org.junit.Test), but it works pretty much the same as...
what's data-reactid attribute in html?
...actid attribute is a custom attribute used so that React can uniquely identify its components within the DOM.
This is important because React applications can be rendered at the server as well as the client. Internally React builds up a representation of references to the DOM nodes that make up you...
Bootstrap full-width text-input within inline-form
...s all form elements gets when they got the class form-control didn't apply if you use the form-inline class on your form.
You could take a look at the bootstrap.css (or .less, whatever you prefer) where you will find this part:
.form-inline {
// Kick in the inline
@media (min-width: @screen-s...
Best documentation for Boost:asio?
...synchronous IO Library.
The examples give more away than the tutorials do. If you don't mind spending a little time looking at the different examples, I would think they should suffice to get you started. If you want to run away with it, then the reference documentation should help you a lot.
Ask ar...
App Inventor 2 数学积木的9个隐藏用法：随机种子、位运算、取整陷阱，踩中...
...—App 崩了。is a number 块判断输入是否为合法数字，配合 if-else 做一层校验，比事后 try-catch 干净得多。
推荐写法：文本框内容 → is a number → true 时走计算逻辑，false 时弹出提示"请输入有效数字"。
高级篇（7-9条）
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Which iomanip manipulators are 'sticky'?
...y Charles:
Exactly! and the only reason that setw appears to behave differently is because there are requirements on formatted output operations to explicitly .width(0) the output stream.
The following is the discussion that lead to the above conclusion:
Looking at the code the following ...
Browser support for URLs beginning with double slash
...'ve recently seen a few links used without a protocol. It didn't seem too difficult to understand - I think it's a great idea and pretty intuitive.
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Increment a value in Postgres
...teger) in a field in a postgres table and increment it by one. For example if the table 'totals' had 2 columns, 'name' and 'total', and Bill had a total of 203, what would be the SQL statement I'd use in order to move Bill's total to 204?
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