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When should I use a composite index?
...olumn_A )
But it will not (at least not directly, maybe it can help partially if there are no better indices) help for queries that need
index( column_A, column_C )
Notice how column_B is missing.
In your original example, a composite index for two dimensions will mostly benefit queries that q...
Properly escape a double quote in CSV
...le double quote to escape a double quote. You can use a command-line tool called csvfix to detect any lines which don't conform: csvfix check -nl -v [filename]
– Sam Critchley
Jun 30 '16 at 14:51
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What data type to use for hashed password field and what length?
...l be unique per user. However, any known salt makes the hash cryptographically weaker than if there were no known salt. A salt only adds value if it is also unknown.
– fijiaaron
May 18 '12 at 13:39
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What data is stored in Ephemeral Storage of Amazon EC2 instance?
...olumes attached when you launch an Amazon EBS-backed instance are automatically deleted when the instance terminates" but you can modify that via configuration.
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Install Marketplace plugin on Eclipse Juno
...asy way to add Eclipse MarketPlace
1. Go to http://eclipse.org/mpc/archive.php and download mpc zip for your eclipse.
2. Than go to Eclipse -> Help -> Install New Software and Add and select Archive file Location
then press ok, it will check dependency and install it.
And Enjoy....
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When should I use Kruskal as opposed to Prim (and vice versa)?
...in a very straightforward way : http://www.thestudentroom.co.uk/showthread.php?t=232168.
Kruskal's algorithm will grow a solution from the cheapest edge by adding the next cheapest edge, provided that it doesn't create a cycle.
Prim's algorithm will grow a solution from a random vertex by adding ...
How to generate sample XML documents from their DTD or XSD?
... tutorial is available here:
http://www.oasis-open.org/committees/download.php/29661/XSD%20and%20jCAM%20tutorial.pdf
And more information on the tool - which is using the OASIS Content Assembly Mechanism (CAM) standard to refactor your XSD into a more XSLT friendly structure - can be found from the...
Setting up FTP on Amazon Cloud Server [closed]
...ce created and have associated an Elastic IP Address to it.
Step #1: Install vsftpd
SSH to your EC2 server. Type:
> sudo yum install vsftpd
This should install vsftpd.
Step #2: Open up the FTP ports on your EC2 instance
Next, you'll need to open up the FTP ports on your EC2 server. Log...
File content into unix variable with newlines
...
The assignment does not remove the newline characters, it's actually the echo doing this. You need simply put quotes around the string to maintain those newlines:
echo "$testvar"
This wil give the result you want. See the following transcript for a demo:
pax> cat num1.txt ; x=$(cat...
What is Java Servlet?
...a particular type of network request - most commonly an HTTP request. Basically servlets are usually used to implement web applications - but there are also various frameworks which operate on top of servlets (e.g. Struts) to give a higher-level abstraction than the "here's an HTTP request, write to...