UPDATE (SQL) Updated 2025-07-16
MySQL Updated 2025-07-16
Create user for further logins without sudo askubuntu.com/questions/915585/how-to-login-mysql-shell-when-mysql-have-no-password/1325689#1325689:
sudo mysql -e "CREATE USER $USER"
Create test user with password:
sudo mysql -e 'CREATE USER user0 IDENTIFIED WITH mysql_native_password BY "a"'
sudo mysql -e 'GRANT ALL PRIVILEGES ON database_name.* TO "user0"'
and login as that user:
mysql -u user0 -p
Login with password given on the command line:
mysql -u user0 -pmypassword
The IDENTIFIED WITH mysql_native_password part is to overcome "Client does not support authentication protocol requested by server" when connecting from Node.js.
List users:
sudo mysql -e 'SELECT * FROM mysql.user'
View permissions for each user on each DB: serverfault.com/questions/263868/how-to-know-all-the-users-that-can-access-a-database-mysql
sudo mysql -e 'SELECT * FROM mysql.db'
List databases:
sudo mysql -e 'SHOW DATABASES'
Create database:
sudo mysql -e 'CREATE DATABASE mydb0'
Destroy database:
sudo mysql -e 'DROP DATABASE mydb0'
Show tables in database:
sudo mysql -e 'SHOW TABLES' mydb0
or:
sudo mysql -e 'SHOW TABLES FROM mydb0'
PostgreSQL Updated 2025-07-16
Had a look at the source tree, and also felt good.
If Oracle is the Microsoft of database, Postgres is the Linux, and MySQL (or more precisely MariaDB) is the FreeBSD (i.e. the one that got delayed by legal issues). Except that their software licenses were accidentally swapped.
The only problem with Postgres is its name. PostgreSQL is so unpronounceable and so untypeable that you should just call it "Postgres" like everyone else.
SQLite Updated 2026-08-21
The minimalism, serverlessness/lack of temporary caches/lack of permission management, Hipp's religious obsession with efficiency, the use of their own pure Fossil version control[ref]. Wait, scrap that last one. Pure beauty!
Official Git mirror: github.com/sqlite/sqlite
Create a table
sqlite3 db.sqlite3 "
CREATE TABLE 'IntegerNames' (int0 INT, char0 CHAR(16));
INSERT INTO 'IntegerNames' (int0, char0) VALUES (2, 'two'), (3, 'three'), (5, 'five'), (7, 'seven');
"
List tables:
sqlite3 db.sqlite3 '.tables'
output:
IntegerNames
Show schema of a table:
sqlite3 db.sqlite3 '.schema IntegerNames'
outputs the query that would generate that table:
CREATE TABLE IF NOT EXISTS 'IntegerNames' (int0 INT, char0 CHAR(16));
Show all data in a table:
sqlite3 db.sqlite3 'SELECT * FROM IntegerNames'
output:
2|two
3|three
5|five
7|seven
SQL COUNT function Updated 2025-07-16
Have a look at some interesting examples under nodejs/sequelize/raw/many_to_many.js.
Spin valve Updated 2025-07-16
Basic component in spintronics, used in both giant magnetoresistance
Giant magnetoresistance Updated 2025-07-16
Video 1.
Introduction to Spintronics by Aurélien Manchon (2020) giant magnetoresistance section
. Source.
Describes how giant magnetoresistance was used in magnetoresistive disk heads in the 90's providing a huge improvement in disk storage density over the pre-existing inductive sensors
Speed of light experiment Updated 2025-07-16
Video 1.
Replicating the Fizeau Apparatus by AlphaPhoenix (2018)
Source. Modern reconstruction with a laser and digital camera.
Video 2.
Visualizing video at the speed of light - one trillion frames per second by MIT (2011)
Source. Fast cameras. OK, this takes it to the next level.
Emission theory (vision) Updated 2025-07-16
It is so mind blowing that people believed in this theory. How can you think that, when you turn on a lamp and then you see? Obviously, the lamp must be emitting something!!!
Then comes along this epic 2002 paper: pubmed.ncbi.nlm.nih.gov/12094435/ "Fundamentally misunderstanding visual perception. Adults' belief in visual emissions". TODO review methods...
Faster-than-light Updated 2025-07-16
One argument of why, is that if you could travel faster than light, then you could send a message to a point in Spacetime that is spacelike-separated from the present. But then since the target is spacelike separated, there exists a inertial frame of reference in which that event happens before the present, which would be hard to make sense of.
Even worse, it would be possible to travel back in time:
20% time rule Updated 2025-07-16
The Google Story suggests that this practice existed in academia, where it was brought from. But I can't find external references to it easily:
At Google, the preference is for working in small teams of three, with individual employees expected to allot 20 percent of their time to exploring whatever ideas interest them most. The notion of "20 percent time" is borrowed from the academic world, where professors are given one day a week to pursue private interests.
eGroups Updated 2025-07-16
Company co-founded by Scott Hassan, early Google programmer at Stanford University, and Carl Victor Page, Jr., Larry Page's older brother.
They were an email list management website, and became Yahoo! Groups after the acquisition.
The company was sold to Yahoo! in August 2000 for $432m and became Yahoo! Groups. They managed to miraculously dodge the Dot-com bubble, which mostly poppet in 2021. After the acquisition, Yahoo started to redirect them to: groups.yahoo.com as can be seen on the Wayback Machine: web.archive.org/web/20000401000000*/egroups.com The first archive of groups.yahoo.com is from February 2001: web.archive.org/web/20010202055100/http://groups.yahoo.com/ and it unsurprisingly looks basically exactly like eGroups.

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