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MQTT接入EasyIoT平台 - 创客硬件开发 - 清泛IT社区，为创新赋能！
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代码差别主要在：地址、端口不同，且使用用户名、密码认证（这里仅仅是演示，隐藏了部分，以实际为准），订阅主题使用上面新建的。
What do I need to do to get Internet Explorer 8 to accept a self signed certificate?
... certificate.”, choose “Continue to this website (not recommended).”
Select Tools➞Internet Options.
Select Security➞Trusted sites➞Sites.
Confirm the URL matches, and click “Add” then “Close”.
Close the “Internet Options” dialog box with either “OK” or “Cancel”.
Refres...
关于我们 · App Inventor 2 中文网，少儿编程陪伴者
... 我家孩子在App Inventor 2 中文网的少儿编程课程中学到了如何设计自己的App，现在他已经可以独立开发一些简单的小应用了。很高兴看到他对于编程的兴趣和自信的提升！ ...
Convert from MySQL datetime to another format with PHP
I have a datetime column in MySQL.
18 Answers
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Not equal != operator on NULL
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As a manual workaround, you could commonly SELECT * FROM MyTable WHERE coalesce(MyColumn, 'x') <> 'x' to assign a constant if it is NULL value, providing you give an appropriate datatype for the sentinel value x (in this case a string/char). This is TSQL syntax ...
Using SSH keys inside docker container
... different base, and each of them begins a new stage of the build. You can selectively copy artifacts from one stage to another, leaving behind everything you don’t want in the final image.
Keeping this in mind here is my example of Dockerfile including three build stages. It's meant to create a...
Bogus foreign key constraint fail
...Two possibilities:
There is a table within another schema ("database" in mysql terminology) which has a FK reference
The innodb internal data dictionary is out of sync with the mysql one.
You can see which table it was (one of them, anyway) by doing a "SHOW ENGINE INNODB STATUS" after the drop f...
I need to store postal codes in a database. How big should the column be?
...nce a block on one side of the street. To find a broader region, you would select the first half of the postal code. Having this information in a separate table really won't help anything and would be more complicated to maintain.
– RevNoah
Dec 2 '13 at 17:08
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MySQL: multiple tables or one table with many columns?
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Recently I was faced with this same problem, because MySQL InnoDB tables have a relatively small length limit (~8000 bytes). In my problem table (data from very lengthy insurance forms, more than 100 columns) we have multiple varchar columns, all UTF8. So we easily filled the ~...
What's the $unwind operator in MongoDB?
...oDB employs an "NoSQL" approach to data storage, so perish the thoughts of selects, joins, etc. from your mind. The way that it stores your data is in the form of documents and collections, which allows for a dynamic means of adding and obtaining the data from your storage locations.
That being sai...