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How to 'insert if not exists' in MySQL?
... any AUTO_INCREMENT column with failed insert. Probably because it's not really failed, but UPDATE'd.
– not2qubit
Oct 29 '13 at 21:36
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一分钟读懂低功耗蓝牙(BLE) MTU交换数据包 - 创客硬件开发 - 清泛IT社区，...
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Servlet for serving static content
...;url-pattern>/</url-pattern>
</servlet-mapping>
This basically just maps all content files by extension to the default servlet, and everything else to "myAppServlet".
It works in both Jetty and Tomcat.
s...
Jquery to change form action
...e jQuery.attr() in your click handler:
$("#myform").attr('action', 'page1.php');
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Difference between VARCHAR and TEXT in MySQL [duplicate]
...R(30) instead of TINYTEXT or TEXT and if someone tries to save the text of all three "Lord of the Ring" books in your phone number column you only store the first 30 characters :)
Edit: If the text you want to store in the database is longer than 65535 characters, you have to choose MEDIUMTEXT or L...
Should I use the datetime or timestamp data type in MySQL?
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Timestamps in MySQL are generally used to track changes to records, and are often updated every time the record is changed. If you want to store a specific value you should use a datetime field.
If you meant that you want to decide between using a UNIX ...
HTTPKeepAlive，开启还是关闭 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...对服务端不得不维持大量的连接。开启还是关闭，这是个问题。
一个经常用来讲解HTTPKeepAlive的例子一般是这样描述的：当我们访问一个包含了若干个图片的网页时，如果HTTPKeepAlive是关闭的，那么页面中每一个图片都会发起一...
load and execute order of scripts
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If you aren't dynamically loading scripts or marking them as defer or async, then scripts are loaded in the order encountered in the page. It doesn't matter whether it's an external script or an inline script - they are executed in the order the...
What is a lambda (function)?
...us and refers to anonymous functions in programming.
Why is this cool? It allows you to write quick throw away functions without naming them. It also provides a nice way to write closures. With that power you can do things like this.
Python
def adder(x):
return lambda y: x + y
add5 = adder(5)...
How to listen for changes to a MongoDB collection?
...tricks. The key here is the oplog.
When you run MongoDB in a Replica Set, all of the MongoDB actions are logged to an operations log (known as the oplog). The oplog is basically just a running list of the modifications made to the data. Replicas Sets function by listening to changes on this oplog a...