Learn7 lessons
SQL
The language every backend job assumes you already know, from SELECT to the joins people get wrong in interviews.
In this course
- SELECTAsking a table for some of its columns, and nothing else.5 min
- WHEREKeeping the rows you want, and the one comparison that never works.6 min
- ORDER BY and LIMITPutting rows in an order, and why they have none until you say so.5 min
- GROUP BY and aggregatesCollapsing many rows into one number, and the difference between WHERE and HAVING.7 min
- JoinsPutting two tables together, and the WHERE clause that silently undoes a LEFT JOIN.8 min
- IndexesWhy a query gets slow, what an index actually is, and how to stop one being used by accident.8 min
- TransactionsAll of it or none of it, and what "isolation" is protecting you from.7 min