大约有 40,000 项符合查询结果（耗时：0.0577秒） [XML]
Does MySQL ignore null values on unique constraints?
...
Yes, MySQL allows multiple NULLs in a column with a unique constraint.
CREATE TABLE table1 (x INT NULL UNIQUE);
INSERT table1 VALUES (1);
INSERT table1 VALUES (1); -- Duplicate entry '1' for key 'x'
INSERT table1 VALUES (NULL);
INSER...
Get selected option from select element
...ted elements use
$("select option:selected").length
To Get the value of all selected elements use
var str = "";
$("select option:selected").each(function () {
str += $(this).text() + " ";
});
share
...
JavaScript validation for empty input field
I have this input field
<input name="question"/> I want to call IsEmpty function when submit clicking submit button.
...
Unable to load DLL 'SQLite.Interop.dll'
Periodically I am getting the following exception:
41 Answers
41
...
Does “untyped” also mean “dynamically typed” in the academic CS world?
...theory". Programming language theory is based on these foundations. And in all these mathematical contexts, "type" has a particular, well-established meaning.
The terminology "dynamic typing" was invented much later -- and it is a contradiction in terms in the face of the common mathematical use of...
Long-held, incorrect programming assumptions [closed]
...
For a long time I assumed that everyone else had this super-mastery of all programming concepts (design patterns, the latest new language, computational complexity, lambda expressions, you name it).
Reading blogs, Stack Overflow and programming books always seemed to make me feel that I was beh...
How does autowiring work in Spring?
...
First, and most important - all Spring beans are managed - they "live" inside a container, called "application context".
Second, each application has an entry point to that context. Web applications have a Servlet, JSF uses a el-resolver, etc. Also, th...
How to prevent UINavigationBar from covering top of view in iOS 7?
After updating to Xcode 5, the navigation bars in all of my app's views have shifted down. Here are some screenshots, the first showing everything in the view as it's pulled down, and the second showing all of it untouched. The search bar should begin where the navigation bar.
...
What's an object file in C?
...t from the compilation phase. It's mostly machine code, but has info that allows a linker to see what symbols are in it as well as symbols it requires in order to work. (For reference, "symbols" are basically names of global objects, functions, etc.)
A linker takes all these object files and comb...
How to prevent Node.js from exiting while waiting for a callback?
...
Callback is Not Queued
Node runs until all event queues are empty. A callback is added to an event queue when a call such as
emmiter1.on('this_event',callback).
has executed. This call is part of the code written by th...