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How to add column if not exists on PostgreSQL?
Question is simple. How to add column x to table y , but only when x column doesn't exist ? I found only solution here how to check if column exists.
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How does deriving work in Haskell?
...se to implement it in its own way. There's lots of work on how to make it extensible however.
Derive is a tool for Haskell to let you write your own deriving mechanisms.
GHC used to provide a derivable type class extension called Generic Classes, but it was rarely used, as it was somewhat weak.
Th...
In Java, what does NaN mean?
...meters
that cause the operation to produce
some undefined result. For example,
0.0 divided by 0.0 is arithmetically undefined. Taking the square root of a
negative number is also undefined.
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What is in your .vimrc? [closed]
...ed inside a .vimrc file. Typical features for a programmer would be syntax highlighting, smart indenting and so on.
72 An...
how to remove untracked files in Git?
I'm working on a branch, say "experimental" branch which I branch out from my master branch.Then, I generate a user model in experimental branch, but does not add them to index yet.
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How can I add numbers in a Bash script?
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For integers:
Use arithmetic expansion: $((EXPR))
num=$((num1 + num2))
num=$(($num1 + $num2)) # Also works
num=$((num1 + 2 + 3)) # ...
num=$[num1+num2] # Old, deprecated arithmetic expression syntax
Using the external expr utili...
How to convert a color integer to a hex String in Android?
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The mask makes sure you only get RRGGBB, and the %06X gives you zero-padded hex (always 6 chars long):
String hexColor = String.format("#%06X", (0xFFFFFF & intColor));
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Apache Prefork vs Worker MPM
...tion at a time// here connection means single user or single request? pls explain
– user1844933
Jun 25 '19 at 7:18
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Fatal error: “No Target Architecture” in Visual Studio
... try to compile my c++ project using Visual Studio 2010 in either Win32 or x64 mode I get the following error:
11 Answers
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What is the easiest way to push an element to the beginning of the array?
...in use:
irb>> a = [ 0, 1, 2]
=> [0, 1, 2]
irb>> a.unshift('x')
=> ["x", 0, 1, 2]
irb>> a.inspect
=> "["x", 0, 1, 2]"
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