As has been mentioned in this article and many previous takedowns of SQL the language, it's a pretty poor approximation of both relational calculus and relation

As has been mentioned in this article and many previous takedowns of SQL the language, it's a pretty poor approximation of both relational calculus and relational algebra. So in that sense, SQL barely has a leg to stand on. If anything, SQL not adhering more closely to those techniques is why query planning is so fraught in modern relational DBs. A language like the one described in TFA would be both closer to the relational model as theorized and probably easier/more consistent to optimize.