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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 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...
Java Enum Methods - return opposite direction enum
... method that returns the opposite direction (the following is not syntactically correct, i.e, enums cannot be instantiated, but it illustrates my point). Is this possible in Java?
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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 find where a method is defined at runtime?
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This is really late, but here's how you can find where a method is defined:
http://gist.github.com/76951
# How to find out where a method comes from.
# Learned this from Dave Thomas while teaching Advanced Ruby Studio
# Makes the cas...
How do you commit code as a different user?
I want to be able to do this for a script. I'm essentially re-creating the entire version history of some code in Git - it currently uses a different version control system. I need the script to be able to add in the commits to Git while preserving the commit's original author (and date).
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Recommended way of making React component/div draggable
...React.createClass({
getDefaultProps: function () {
return {
// allow the initial position to be passed in as a prop
initialPos: {x: 0, y: 0}
}
},
getInitialState: function () {
return {
pos: this.props.initialPos,
dragging: false,
rel: null // position...
What is meaning of boolean value returned from an event-handling method in Android
... in the rest of the events in that gesture. A "gesture" in this case means all events until the final ACTION_UP or ACTION_CANCEL. Returning false from an ACTION_DOWN means you do not want the event and other views will have the opportunity to handle it. If you have overlapping views this can be a si...