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Difference between Key, Primary Key, Unique Key and Index in MySQL
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Primary key does not allow NULL values, but unique key allows NULL values.
We can declare only one primary key in a table, but a table can have multiple unique keys (column assign).
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Why do we copy then move?
...uestions, one thing you seem to be getting wrong: taking by value in C++11 does not always mean copying. If an rvalue is passed, that will be moved (provided a viable move constructor exists) rather than being copied. And std::string does have a move constructor.
Unlike in C++03, in C++11 it is oft...
Android Writing Logs to text File
...is answer to log to file. Note that from
Android 4.2, READ_LOGS permission doesn't have any impact and every
Application (unless phone is rooted) could only read its own logs.
The disadvantage here is logcat buffer is circular and has a size
limit. You might not get earlier logs.
Use microlog4andro...
How do I invoke a Java method when given the method name as a string?
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Wrong. Yes, getDeclaredMethod does work with private and protected methods. BUT: it does not work with methods defined in superclasses (inherited methods). So, it depends strongly on what you want to do. In many cases you want it to work regardless of the...
Is it possible to set the stacking order of pseudo-elements below their parent element? [duplicate]
...one, and it wasn't even an answer at the time - it was a comment saying it doesn't work.
– BoltClock♦
May 26 '14 at 1:18
1
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How do I split a string with multiple separators in javascript?
...>>> bit = bits[bits.length - 1]
"world!"
... and if the pattern doesn't match:
>>> bits = "Hello awesome, world!".split(/foo/)
["Hello awesome, world!"]
>>> bits[bits.length - 1]
"Hello awesome, world!"
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Convert a list of data frames into one data frame
...troduced in the data.table package version 1.8.2, with a remark that "This does the same as do.call("rbind",l), but much faster". How much faster?
library(rbenchmark)
benchmark(
do.call = do.call("rbind", listOfDataFrames),
plyr_rbind.fill = plyr::rbind.fill(listOfDataFrames),
plyr_ldply = ...
Command to escape a string in bash
...orld" is not escaped to "hello\ world" - printf aproach in accepted answer does that.
– vchrizz
Jan 24 '16 at 21:01
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How do I measure request and response times at once using cURL?
...url -w "@curl-format.txt" -o NUL -s "http://wordpress.com/"
What this does:
-w "@curl-format.txt" tells cURL to use our format file
-o /dev/null redirects the output of the request to /dev/null
-s
tells cURL not to show a progress meter
"http://wordpress.com/" is
the URL we are requesting. ...
Font size in CSS - % or em?
...en width of 640px, but appears as 320 "CSS" pixels (DPR=2). So the website does not appear smaller!
– Benjamin
Feb 28 '18 at 13:30
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