Reddit mentions of SQL QuickStart Guide: The Simplified Beginner's Guide To SQL

Re-iterating what the previous posters said: the fundamentals are the same regardless of system. Learning how to get data out of a SQL system is all about learning how to write SQL.

To effectively learn how to write SQL for data engineering, I highly recommend grabbing a book like one of these*:

1. SQL Quickstart Guide
   
2. SQL Queries
   
3. If you're an experience programmer maybe T-SQL Fundamentals (Microsoft flavor SQL)
   
   and grabbing a sample database for the system of your choice:
   
   
4. MySQL sample Employee db
   
5. PostgreSQL sample dbs
   
6. SQL Server - stackoverflow db
   
   and then practice some of your chosen book on the sample db.
   
   Notes and words of warning:
   
   

• Writing SQL for data engineering or programming is really different than "database administration." A lot of resources on the web are geared towards DBAs and it probably won't help you out much.
  
• University courses on databases tend to be more theoretical than practical, for the sake of learning how to write SQL. University isn't a super efficient method of learning to write SQL.
  
  ^((*I'm not affiliated w/ any of those books))