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Unique constraint that allows empty values in MySQL
...reference (version 5.5).
A UNIQUE index creates a constraint 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 NU...
How do I write a custom init for a UIView subclass in Swift?
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The init(frame:) version is the default initializer. You must call it only after initializing your instance variables. If this view is being reconstituted from a Nib then your custom initializer will not be called, and instead the init?(coder:) version will be called. Since Swift now req...
CSS Selector “(A or B) and C”?
... syntax?
No. CSS' or operator (,) does not permit groupings. It's essentially the lowest-precedence logical operator in selectors, so you must use .a.c,.b.c.
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When to use SELECT … FOR UPDATE?
... a DML query creates a copy of the record (in one or another way) and generally readers do not block writers and vice versa. For these databases, a SELECT FOR UPDATE would come handy: it would lock either SELECT or the DELETE query until another session commits, just as SQL Server does.
When sh...
Easiest way to upgrade eclipse 3.7 to 4.2 (Juno)
...4.2 instead of 3.7, what is the easiest way to upgrade to it, short of installing a separate copy of juno and re-installing all my existing plugins from 3.7 into it?
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throw new std::exception vs throw std::exception
...xceptions is to throw an exception object and to catch it by reference (usually const reference). The C++ language requires the compiler to generate the appropriate code to construct the exception object and to properly clean it up at the appropriate time.
Throwing a pointer to a dynamically alloca...
php中json_decode()和json_encode()的使用方法 - 更多技术 - 清泛网 - 专注C/C++及内核技术
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echo "Unicode: ", json_encode($a, JSON_UNESCAPED_UNICODE), "\n";
echo "All: ", json_encode($a, JSON_HEX_TAG | JSON_HEX_APOS | JSON_HEX_QUOT | JSON_HEX_AMP | JSON_UNESCAPED_UNICODE), "\n\n";
$b = array();
echo "Empty array output as array: ", json_encode($b), "\n";
echo "Empty array out...
PHP shell_exec() vs exec()
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shell_exec returns all of the output stream as a string. exec returns the last line of the output by default, but can provide all output as an array specifed as the second parameter.
See
http://php.net/manual/en/function.shell-exec.php
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How can I change the text inside my with jQuery?
I have a really simple question but it's something I have not done before. I have the following:
4 Answers
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What is a 'semantic predicate' in ANTLR?
...er: it parses an input string consisting of at least
// one number, optionally followed by zero or more comma's and numbers
parse
: number (',' number)* EOF
;
// matches a number that is between 1 and 3 digits long
number
: Digit Digit Digit
| Digit Digit
| Digit
;
// matches a si...