SQLite3 Quirks

CHAR & VARCHAR do not exist

VARCHAR gets treated as TEXT

Primary Keys get some additional automagic functionality when they are INTEGER
 1) They autoincrement
plus Something Weird?

Reminder of the b******g obvious in SQL

1) Foreign Key : a column (or a combination of columns) whose values match a Primary Key in a different table.

i.e. There has to be a Primary Key in this table which matches the foreign key in that table (or vice versa)

Someone else's looser definition:
A foreign key is a column (or columns) that references a column (most often the primary key) of another table. The purpose of the foreign key is to ensure referential integrity of the data. In other words, only values that are supposed to appear in the database are permitted.

i.e attributes in table A must hold a value listed in table B

2) All values in a Primary Key have to be unique

The Briefest-possible Beginner's Guide to Mercurial Distributed Version Control System

Mercurial commands

hg log 

show list of commits

hg diff

show lines which differ between tip and working copy

hg diff -c <commit number>

show diffs caused by commit number - commit number shown in log

hg update <commit number>

set working copy to state of given commit

hg update tip

update to latest commit

hg tag <tag-name> 

mark last commit with a tag - When you have a version you're happy with, tag it

hg update <tag-name>

retrieve tagged commit to working copy

i.e. "update your working copy to match a given previous version"

only possible if there are no uncommitted changes   

hg clone <working copy path>

places a clone of the the working copy in the current directory

i.e.

in Mercurial 

 

How to Switch off a second monitor

I wanted to switch off my second monitor on my Windows 7 Home Premium PC, so that I could connect in to my dev PC, using VNC on a Chromebook.

If I keep an extended desktop on the dev PC, then there is a lot of screen to scroll across on the Chromebook.

I wanted to preserve the settings for the second monitor, so that I did not have to spend a lot of time, re-configuring the second monitor to be just the way I liked it when I started using it again.

The answer turned out to be really simple.

How to turn off your second monitor in Windows 7, without losing the settings for it :

Windows key  + p
Change from "Extend" to "Duplicate" in the onscreen dialog.
Power off the second monitor.

To returnback to the original settings, simply
Windows key + p
Change from "Duplicate" to "Extend"
And remember to switch the monitor back on!  :-)