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MQTT与TCP的区别 - 创客硬件开发 - 清泛IT社区，为创新赋能！
...ard、sysadmin api、插件扩展、对topic或session或clientid的tracing调试等高级功能，大大简化服务器端的开发工作量。实际应用中，只需要写发布和订阅接口函数即可，中间过程对应用开发人员透明。12. 可以通过MQTT over websocket来穿越防...
Rank function in MySQL
... (SELECT @curRank := 0) r
ORDER BY age;
The (SELECT @curRank := 0) part allows the variable initialization without requiring a separate SET command.
Test case:
CREATE TABLE person (id int, first_name varchar(20), age int, gender char(1));
INSERT INTO person VALUES (1, 'Bob', 25, 'M');
INSERT I...
Facebook Post Link Image
When someone posts a link on facebook, a script usually scans that link for any images, and displays a quick thumbnail next to the post. For certain URLs though (including mine), FB doesn't seem to pick up anything, despite their being a number of images on that page.
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How can I remove a key and its value from an associative array?
...oop, then you need to prepend an ampersand to your enumeration variable to allow write access.
– FreeAsInBeer
Jul 30 '12 at 21:20
1
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Python append() vs. + operator on lists, why do these give different results?
...quences) by concatenating the element. The append-method however does literally what you ask: append the object on the right-hand side that you give it (the array or any other object), instead of taking its elements.
An alternative
Use extend() if you want to use a function that acts similar to the ...
How do I see the extensions loaded by PHP?
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Running php -m will give you all the modules, and php -i will give you a lot more detailed information on what the current configuration.
share
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improv...
Count Rows in Doctrine QueryBuilder
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He accepted your answer so I guess all is well. I was under the impression that he only wanted a count without the overhead of actually retrieving the rows which my example shows. There is of course no reason why where conditions could not be added.
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Convert pem key to ssh-rsa format
...m assuming no password for the keys (which is bad).
Generate an RSA pair
All the following methods give an RSA key pair in the same format
With openssl (man genrsa)
openssl genrsa -out dummy-genrsa.pem 2048
In OpenSSL v1.0.1 genrsa is superseded by genpkey so this is the new way to do it (man...
Limit file format when using ?
...tioned here, but is not the default in the dropdown. The default filter is All files (*).]
You can also use asterisks in MIME-types. For example:
<input type="file" accept="image/*" /> <!-- all image types -->
<input type="file" accept="audio/*" /> <!-- all audio types --&g...
Should I use encodeURI or encodeURIComponent for encoding URLs?
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It depends on what you are actually wanting to do.
encodeURI assumes that the input is a complete URI that might have some characters which need encoding in it.
encodeURIComponent will encode everything with special meaning, so you use it for components ...