-- composite key - using two or more existing columns within a table to create a primary key
create table person (
firstName varchar(100) not null,
lastName varchar(100) not null,
dob DateTime not null,
ssn varchar(9) not null,
primary key (firstName, lastName, dob)
)
Enable utf8 pragma
In order to enable utf8 pragma in one-liner, perl interpreter should be called with -Mutf8 option:
perl -Mutf8 -E 'my $人 = "human"; say $人'
Unicode handling with -C switch
The -C command line flag lets you control Unicode features. It can be followed by a list of o...
Use git revert to revert existing commits, especially when those commits have been pushed to a remote repository. It records some new commits to reverse the effect of some earlier commits, which you can push safely without rewriting history.
Don't use git push --force unless you wish to bring down ...
You cam amend the time of a commit using
git commit --amend --date="Thu Jul 28 11:30 2016 -0400"
or even
git commit --amend --date="now"
If you make a commit as the wrong author, you can change it, and then amend
git config user.name "Full Name"
git config user.email "[email protected]"
git commit --amend --reset-author
using System;
using System.Runtime.InteropServices;
namespace ComLibrary
{
[ComVisible(true)]
public interface IMainType
{
int GetInt();
void StartTime();
int StopTime();
}
[ComVisible(true)]
[ClassInterface(ClassInterfaceType.N...
The regular composition works for unary functions. In the case of binary, we can define
(f .: g) x y = f (g x y) -- which is also
= f ((g x) y)
= (f . g x) y -- by definition of (.)
= (f .) (g x) y
= ((f .) . g) x y
Thus,...
you can use -c <name>=<value> to add a configuration only for one command.
To commit as an other user without having to change your settings in .gitconfig :
git -c user.email = mail@example commit -m "some message"
Note: for that example you don't need to precise both user...
In order to use compression over the wire for a faster transfer, pass the --compress option to mysqldump. Example:
mysqldump -h db.example.com -u username -p --compress dbname > dbname.sql
Important: If you don't want to lock up the source db, you should also include --lock-tables=false. But ...
Sometimes it happens that a file was being tracked by git, but in a later point in time was added to .gitignore, in order to stop tracking it. It's a very common scenario to forget to clean up such files before its addition to .gitignore. In this case, the old file will still be hanging around in th...
Git shortlog is used to summarize the git log outputs and group the commits by author.
By default, all commit messages are shown but argument --summary or -s skips the messages and gives a list of authors with their total number of commits.
--numbered or -n changes the ordering from alphabetical (...
.git/hooks/pre-commit
#!/bin/sh
if [ -s pom.xml ]; then
echo "Running mvn verify"
mvn clean verify
if [ $? -ne 0 ]; then
echo "Maven build failed"
exit 1
fi
fi
To setup a WebRTC-based communication system, you need three main components:
A WebRTC signaling server
To establish a WebRTC connections, peers need to contact a signaling server, which then provides the address information the peers require to set up a peer-to-peer connection. Signaling serv...
Interfaces can seem abstract until you seem them in practice. The IComparable and IComparable<T> are great examples of why interfaces can be helpful to us.
Let's say that in a program for a online store, we have a variety of items you can buy. Each item has a name, an ID number, and a price.
...
There are two possible ways of including LaTeX preamble commands (e.g. \usepackage) in a RMarkdown document.
1. Using the YAML option header-includes:
---
title: "Including LaTeX Preample Commands in RMarkdown"
header-includes:
- \renewcommand{\familydefault}{cmss}
- \usepacka...
Most websites require a much more complicated process than the one demonstrated above.
Common steps for logging into a website are:
Get the unique cookie from the initial login form.
Inspect the login form to see what the destination url is for the authentication request
Parse the login form t...
