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Why does PostgreSQL perform sequential scan on indexed column?
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If the SELECT returns more than approximately 5-10% of all rows in the table, a sequential scan is much faster than an index scan.
This is because an index scan requires several IO operations for each row (look up the row in the index, then retrieve the row from the heap). Whe...
How to display hidden characters by default (ZERO WIDTH SPACE ie. ​)
...ing problems with parsing config file of my app... I discovered it accidentally in vi.
2 Answers
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How to forward declare a C++ template class?
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I disagree. The standard says: "A template-parameter shall not be given default arguments by two different declarations in the same scope". And I found nothing about defaults in the first declaration only. Also the code with the forward declaration and defaults in the definition ...
How do I update zsh to the latest version?
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If you have Homebrew installed, you can do this.
# check the zsh info
brew info zsh
# install zsh
brew install --without-etcdir zsh
# add shell path
sudo vim /etc/shells
# add the following line into the very end of the file(/etc/shells)
/usr/loc...
jQuery .hasClass() vs .is()
... Just because a function has less funtionality does NOT mean it's automatically faster.
– Kris
Feb 4 '11 at 19:54
15
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how to add records to has_many :through association in rails
...ata from the joint table Agents without having N+1 bug example displaying all the houses and corresponding agents for the given customer
– Ankita.P
Jul 24 '15 at 11:00
add a ...
How to pass a function as a parameter in Java? [duplicate]
...u have a class or interface with only a single abstract method (sometimes called a SAM type), for example:
public interface MyInterface {
String doSomething(int param1, String param2);
}
then anywhere where MyInterface is used, you can substitute a lambda expression:
class MyClass {
publ...
Providing a default value for an Optional in Swift?
...he idiom for dealing with optionals in Swift seems excessively verbose, if all you want to do is provide a default value in the case where it's nil:
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Reflecting parameter name: abuse of C# lambda expressions or syntax brilliance?
...type inference can do that). This can be expressed in the CLR. But F# disallows it, mostly because if you did that, those APIs would not be callable from C#.) When it comes to interop, there are always trade-offs at 'edge' features regarding what benefits you get versus what interop you trade awa...
Why can I not push_back a unique_ptr into a vector?
...to a local variable. The lifetime of a local variable is managed automatically: local variables are destroyed when the block ends (e.g., when the function returns, in this case). You need to dynamically allocate the object:
std::unique_ptr<int> ptr(new int(1));
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