Practical SQL for Data Analysis (via) This is a really great SQL tutorial: it starts with the basics, but quickly moves on to a whole array of advanced PostgreSQL techniques - CTEs, window functions, efficient sampling, rollups, pivot tables and even linear regressions executed directly in the database using regr_slope(), regr_intercept() and regr_r2(). I picked up a whole bunch of tips for things I didn't know you could do with PostgreSQL here.