SQLite teaches virtually all of the necessary concepts to jump right into a multi-user RDBMS, even most of the syntax, with the exception of being more lax about datatypes. My audience is not people intending to build applications, but to do data analysis beyond what they can do in your typical spreadsheet. I don't think the PHP vs. Python analogy is particularly accurate. I don't feel that PHP is easier to learn than Python unless the main goal is to produce something public-facing on the web. Nevermind that the syntax is significantly different.