Ciro Santilli @cirosantilli  40

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Superconducting qubit type Updated 2025-07-16

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Stars nearest to the Sun Updated 2025-07-16

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Figure 2.
Distance of stars nearest to the Sun as function of time
. Source.

upload.wikimedia.org/wikipedia/commons/e/e9/Near-stars-past-future-en.svg

Some notable ones:

Proxima Centauri, the nearest one, at 4 ly. It is part of the Alpha Centauri star system, which contains two other stars at very similar distances as well, and their relative distances to earth will change positions in a few tens of thousands of years.
Sirius, the brightest star in the sky at 9 ly

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JTAG Updated 2025-07-16

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Covert Lab Updated 2025-07-16

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www.covert.stanford.edu/

Makes the E. Coli Whole Cell Model by Covert Lab.

Lead: Markus W. Covert.

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Closure table Updated 2025-07-16

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Nested set model Updated 2025-07-16

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This is particularly important in SQL: Nested set model in SQL, as it is an efficient way to transverse trees there, since querying parents every time would require multiple disk accesses.

The ASCII art visualizations from stackoverflow.com/questions/192220/what-is-the-most-efficient-elegant-way-to-parse-a-flat-table-into-a-tree/194031#194031 are worth reproducing.

As a tree:

Root 1
- Child 1.1
  - Child 1.1.1
  - Child 1.1.2
- Child 1.2
  - Child 1.2.1
  - Child 1.2.2

As the sets:

 __________________________________________________________________________
|  Root 1                                                                  |
|   ________________________________    ________________________________   |
|  |  Child 1.1                     |  |  Child 1.2                     |  |
|  |   ___________    ___________   |  |   ___________    ___________   |  |
|  |  |  C 1.1.1  |  |  C 1.1.2  |  |  |  |  C 1.2.1  |  |  C 1.2.2  |  |  |
1  2  3___________4  5___________6  7  8  9___________10 11__________12 13 14
|  |________________________________|  |________________________________|  |
|__________________________________________________________________________|

Consider the following nested set:

0, 8, root
  1, 7, mathematics
    2, 3, geometry
      3, 6, calculus
        4, 5, derivative
        5, 6, integral
      6, 7, algebra
  7, 8, physics

When we want to insert one element, e.g. limit, normally under calculus, we have to specify:

parent
index within parent

so we have a method:

insert(parent, previousSibling)

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SQL transaction isolation level Updated 2025-07-16

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Each transaction isolation level specifies what can or cannot happen when two queries are being run in parallel, i.e.: the memory semantics of the system.

Remember that queries can affects thousands of rows, and database systems like PostgreSQL can run multiple such queries at the same time.

Good summary on the PostgreSQL page: www.postgresql.org/docs/14/transaction-iso.html

Implementation specifics:

SQLite isolation levels

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SQL standard version Updated 2025-07-16

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GROUP BY (SQL) Updated 2025-07-16

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INSERT (SQL) Updated 2025-07-16

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JOIN (SQL) Updated 2025-07-16

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SELECT (SQL) Updated 2025-07-16

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UPDATE (SQL) Updated 2025-07-16

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MySQL Updated 2025-07-16

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sudo mysql

works on Ubuntu 20.10.

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"

Run command from CLI stackoverflow.com/questions/1602904/how-do-you-run-a-single-query-through-mysql-from-the-command-line

mysql -e 'SHOW DATABASES'

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

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'

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PostgreSQL Updated 2025-07-16

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PostgreSQL feels good.

Its feature set is insanely large! Just look at stuff like: stackoverflow.com/questions/1986491/sql-split-string-by-space-into-table-in-postgresql/1993058#1993058

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.

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Microsoft SQL Server Updated 2025-07-16

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SQLite Updated 2026-08-21

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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

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SQL COUNT function Updated 2025-07-16

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Have a look at some interesting examples under nodejs/sequelize/raw/many_to_many.js.

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Spin valve Updated 2025-07-16

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Basic component in spintronics, used in both giant magnetoresistance

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Tunnel magnetoresistance Updated 2025-07-16

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Video 1.

What is spintronics and how is it useful? by SciToons (2019)

Source. Gives a good 1 minute explanation of tunnel magnetoresistance.

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