For those trying to up their SQL game from basic selects and grouping, I suggest learning:

- Common Table Expressions (CTEs). They will equip you to write clean, organized, and expressive SQL.

- CREATE TABLE AS SELECT. This command powers SQL-driven data transformation.

- Window functions, particularly SUM, LEAD, LAG, and ROW_NUMBER. These enable complex calculations without messy self-joins.

Learning those three will change your relationship with SQL and blow the door open of problems you can solve with the language.