Query planners often choose the algorithm based on data statistics (as described in the article). Compilers generally just make a lot of constant-factor improv

Query planners often choose the algorithm based on data statistics (as described in the article). Compilers generally just make a lot of constant-factor improvements without changing the algorithm. One exception might be the tail-call optimization, which changes the space complexity of an algorithm. And that's one of the optimizations where the developer needs to know for sure whether it will br applied or not.