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Subqueries vs joins
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Here's an example of how subqueries are evaluated in MySQL 6.0.
The new optimizer will convert this kind of subqueries into joins.
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Determine if running on a rooted device
...has a certain piece of functionality that will only work on a device where root is available. Rather than having this feature fail when it is used (and then show an appropriate error message to the user), I'd prefer an ability to silently check if root is available first, and if not,hide the respect...
Python - Get path of root project structure
I've got a python project with a configuration file in the project root.
The configuration file needs to be accessed in a few different files throughout the project.
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How to export a Vagrant virtual machine to transfer it
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Does the "clean way" account for databases (mySQL, Wordpress) that might be inside the vm? How can that be synced over to the other pc?
– kevllar
Feb 17 '16 at 4:33
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Is storing a delimited list in a database column really that bad?
...ient table-scan. May have to resort to regular expressions, for example in MySQL:
idlist REGEXP '[[:<:]]2[[:>:]]'*
Hard to count elements in the list, or do other aggregate queries.
Hard to join the values to the lookup table they reference.
Hard to fetch the list in sorted order.
To solve th...
Socket send函数和recv函数详解以及利用select()函数来进行指定时间的阻塞 ...
...有情况下，发送开始调用是局部的：无论其它进程的状态如何，它立刻返回。如果这个调用使得一些系统资源用完，那么它将失败并返回 一个错误代码。高质量的MPI实现应保证这种情况只在“病态”时发生。即，一个MPI实现将...
Edit the root commit in Git?
...t you have a clean working tree, you can do the following.
# checkout the root commit
git checkout <sha1-of-root>
# amend the commit
git commit --amend
# rebase all the other commits in master onto the amended root
git rebase --onto HEAD HEAD master
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App Inventor 2 低功耗蓝牙 BlueToothLE 拓展 · App Inventor 2 中文网
... Disconnect 或 DisconnectWithAddress 引起的，或者在设备移开或重置以致发生连接丢失后引起的。
FloatsReceived – 当从连接的蓝牙设备接收到一个或多个 IEEE 754 浮点值时，将触发该事件。根据上次调用 ReadFloats 或 RegisterForFlo...
Insert a commit before the root commit in Git?
...s empty commit
We’ll put the new empty commit on a temporary branch newroot for convenience.
1. Create a new empty commit
There is a number of ways you can do this.
Using just plumbing
The cleanest approach is to use Git’s plumbing to just create a commit directly, which avoids touching th...
What is sharding and why is it important?
...cross multiple logical or physical nodes (in the case of my understanding (mySQL) multiple databases, most likely housed on different logical hardware). Horizontal partitioning is a less specific term, of which "Sharding" is a subset. Again using mySQL as an example, a mySQL partition is handled by...