5 lessons
DDL: defining the structure of your data
CREATE, ALTER and DROP - the SQL commands that build and change the shape of your database, plus every constraint that keeps data honest.
DML: inserting, updating and deleting rows
INSERT, UPDATE and DELETE in depth, plus why every one of them should almost always be wrapped in a transaction.
SELECT: reading data the way you'll do it most
The anatomy of a SELECT statement, the order it actually executes in, sorting, and paging through results.
Filtering and pattern matching text
LIKE, wildcards, regular expressions, and why searching text inside a database is a different problem from searching numbers.
Set operations and built-in functions
UNION, INTERSECT and EXCEPT for combining query results, plus the string, date and NULL-handling functions you'll use in nearly every real query.