Both stories feature unconventional heroes, are in rather absurd situations, and feature a twisted sense of humor. They are both great comedies with brilliant actors!
They are both really good police-comedy movie even tho the story is totally different, if you liked one you will definitely like the other one
The subject matter and plot lines of these have absolutely nothing in common, but both are parodies and I found the tone and humor to be really similar. Comedy is all about personal taste, but if you like yours deadpan and absurd with a touch of suspense and enjoyed Going by the Book you should give Once Upon a Time in Saengchori a try. I find them both pee-your-pants funny.