Are you looking to enhance your data skills and become proficient in SQL? We just posted a comprehensive, 11-hour SQL course on the freeCodeCamp.org YouTube channel. It will teach you to handle complex database queries. (Vlad Gheorghe)

A giant course going over many of the 'functions' of SQL. Good but long, and you will need to consult additional sources to connect many of the concepts to the bigger picture.

Learn SQL. Interactive 'book', light-weight and intends to be the 'best place on the internet for learning SQL'.

Looks awesome to learn!

Use SQL queries to solve the murder mystery. Suitable for beginners or experienced SQL sleuths.

Lean SQL with a murder-mystery game. How cool!

A whole recommendation flood of going about sql learning. Syntax, Fundamentals, some advanced advice. Can be used to comfortably build a personal learning path.

A straightforward page containing SQL tutorials, guides and quizzes. If wanting to grok SQL quickly and efficiently this seems like one of the best ways to go about it in a weekend or over a couple evenings.

Steampipe is an open source tool to instantly query your cloud services (e.g. AWS, Azure, GCP and more) with SQL. No DB required.

A simple yet powerful tool to analyze and show the path of queries

A detailed and useful guide for the migration process.
Also contains a link to a similar guide from postgres 13 to 14, where some password modification is needed.

Postgres docker containers have a problem of multiple restarts.
A simple way to check for them being 'up' up (i.e. initialized, reachable, and ready) is not through pg_isready but instead by checking on the set database port (default 5432) if a connection can be established.

It will not send anything back really since it's not designed as an http server. So curl -sFfI db:5432 for example will get back 52 Empty Reply with status code 52. If you want to check with that make sure to compare to error code 52!

The easiest option if another container has to wait for this one to start up (and especially in a docker stack environment where no wait_for option exists) is:
nc db 5432 which will only return true when the port is ready.

An example for the nextcloud fpm container waiting for database readiness:
entrypoint: sh -c "while !(nc -z db 5432); do sleep 1; done; /entrypoint.sh php-fpm"

Very nice introductory page to SQLite, how to work with it, its peculiarities and so on.