I started out the quarter really looking forward to what Professor Rosario had in store for CS 143 because of his modern approach and industry experience, but ended up disliking him and my life while taking this class.

Projects:

Credit to him here, the projects are practical and interesting. The 2nd project is fairly vague but doable if you start early.

Tests:

He wanted to be like Eggert but honestly he couldn't. Eggert at least gives somewhat fair tests, Rosario's tests were the biggest load of BS. Especially the final, a huge test where he handpicked the most random stuff out of his lecture slides and made it a large portion of the test. The final was the one of the hardest tests I've taken here at UCLA and it felt like he made the test unnecessarily hard.

Piazza:

He seems like an okay guy in person, but he can be seriously mean to students asking FAIR questions online. I wasn't even a victim of this but monitored Piazza frequently and it felt like he was going on some weird power trip.

Overall, I wouldn't recommend him for 143, it's not the worth the stress and the hassle. This is the first time I've felt compelled enough to write a BruinWalk review about a professor. He's clearly a smart guy but out to get students to fail his tests.

I was recommended this class specifically with this professor because he was supposed to be "amazing". This couldn't be any further from the truth. He has roughly 100 slides a lecture to go through at 8 AM in the morning. The slides are actually dense and whenever he was asked to explain something he always had no clue how any technical stuff really worked. Seems absolutely incompetent in any theoretical concepts to the point where he had to "get mad" and just move one due to his lack of knowledge. His homework and projects were fairly reasonable but were exceptionally vague. Anything you would ask on piazza would always receive a ridiculously sarcastic and demeaning reply. Never have I seen this much god damn toxicity in a piazza forum in finals week. His midterm is exceptionally long for the time given to us. The final was absolutely absurd. It seems like he just sat there the night before the final and specifically chose the topics that he said weren't going to be on the final or was incapable of being able to explain during lecture and designed a test around those concepts. Is he a good person in normal life...who knows? All I know is he needs to change how he goes about his teaching or just stay in industry.

TL;DR Rosario has industry experience, so that's a plus. But that comes with quite a bit of arrogance, inconsistency, and poor awareness. There's been some enjoyable lectures, and I've had worse professors. Rosario has a ways to improve, but for now, learning doesn't correlate to getting a good grade, so taking R-cubed may be more pain than it's worth.
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The class is weird. "R-cubed" is a friendly professor, but looking back, his class was not very useful. His lectures were not very relevant nor helpful. and he penalized students for not attending. I scored 2 stddev above median in midterm and fully expected an A in the class, but somehow scored below the median on the final, due to some very very strange questions that I could only assume were lecture-only.

He also has a poor attitude on Piazza, even referring to students as "entitled" when they ask for clarifications on his very confusing projects and examinations. He doesn't seem to recognize how his comments could be detrimental to mental health during the stress-packed finals week. He tries to be helpful, but is a flawed human with a lack of self-awareness in educating.

To his credit, he is a newer professor who's been in industry a lot, and I appreciate that he has such high standards for his students. I would be wary about taking his class, but it's pretty good if you're self-reliant and don't mind inconsistent grading.

This was honestly one of the weirdest classes I've ever taken. The class started out extremely easy...the first project was a joke (easier than a CS31 project) and the midterm was very straightforward and fair.
However, once we moved on from SQL and started learning about more theory-intensive subjects, the entire class went completely downhill. Our second project was an absolute shit show. For some people, just RUNNING the project took 10+ hours since we were dealing with big data...and while we did learn very valuable information about Spark, I feel like there would've been a more efficient way to teach us this material. Additionally, one of the things that annoyed me the most was that he would not give us concrete methods to approach a problem...he would say things like "oh it won't show up on exams don't worry about it" which was extremely frustrating as a student. His homework assignments were horrible...they made no sense and needed a lot of clarification (you should've seen our Piazza LMAO). Our final was also the hardest test I've taken at UCLA and half the material was from like 1 or 2 slides from his powerpoints.
Overall, this class was okay. I learned very valuable information (esp SQL) and would definitely recommend to take it before you graduate. However, this class with Rosario was just extremely frustrating because of the lack of clarification in a lot of his projects/assignments. Don't get me wrong—Rosario was a great lecturer and his slides were very helpful (I really loved attending his lectures and he was very responsive on Piazza). I just didn't like his assignments and the overall structure of the class.

Bad!!!!!!!!

---TLDR---
In my opinion, Rosario's intentions aren't expressly bad, but he often acts in ways that don't help anyone. He frequently characterizes things he doesn't seem to really understand as 'unnecessary', 'impractical', and 'not relevant to industry'. He frequently tries to act cool - and sometimes is cool - but often simply acts in unreasonable ways.
Most of the things I wanted to say are already written on bruinwalk, but here's some more stories.
---Stories---
When discussing some dependency stuff, topological sort came up and he made a mistake in explaining the material. Mistakes are honestly fine, but what isn't fine is that when a student questioned it during lecture, he quickly disregarded it and became increasingly upset as more students realized he didn't know what he was talking about. He then proceeded to yell at the student, rush through the slides, and then, near the end, reference his meme of a crying baby to state that everyone is picking on him (the "picking on" text was underneath a picture of a crying baby on the slides). I guess people have their off-days and its not a big deal, but he refused to ever clarify the material, and then put a question on the final regarding it. I feel that's not very cool of him.
I might give him a pass for this whole topological sort fiasco if it weren't for the fact that for the midterm, he said "we will only make passing reference to them" regarding recursive and window queries! And then he put them both on the midterm! (Rosario often says that he fully specifies what is on his exams - this is not true, do not believe it.)
Moreover, he said in office hours once that triggers and constraints will be extremely important for the test, but they only came up as a tangentially for one out of 200 points!
Also, he said that B+-Trees were not to be tested (because he severely messed up teaching the topic, and was unable to explain the difference between a B+-Tree and a B-Tree during lecture, and even the homework on the subject was broken because the insertion-style was ambiguous and inconsistent lol), but then it was on the final.
Calculating the value for hyperloglog was on the final. Calculators were not allowed, so we were expected to compute a*m^2*Z where Z = 1/sum_{j=0}^m 1/2^{c_j} and then round only at the last step? Honestly I don't know what that formula means, I just copied it from the slides right now. I left that question blank on the final because I didnt have the formula lol.
Oh also, imo, his slides are very unclear. just fyi. I relied on other school's notes the entire quarter tbh.
---Reddit information---
Before you take a class under this professor, be aware of this (seems that Rosario reported a student to the police regarding a discussion on reddit?) https://removeddit.com/r/Professors/comments/bzyco2/the_attendance_dilemma/ercowpa/?context=3
---Final distribution info---
For anyone looking for stats regarding the final, a 100/200 is a B, mean/median is 42%, high is 72%

So I signed up the account just for this professor, I got a bad grade in this class but don't get me wrong I get B+ for other cs courses as well but this grade is really not what i was expecting.
Projects: To be fair, the projects are interesting and I actually enjoy doing them. However the timeline RRR set up was ridiculous. For project 1A we have two weeks just to load the data, and for the same amount of time we are asked to do a much harder task.
Exam: Midterm is fair, we are tested on SQL queries and related stuff, fully expected. BUT THE FINAL, it was a disaster. For the final RRR tried really hard to make the questions in an eggert style but failed. We were not given any practice tests and the content was just randomly picked from the lecture slides... the average was around 84/200. And one of my friends just told me for the final he "expected" us to do better (maybe because he thought the questions were easy?) but as you can see from our average they weren't. So he just made the average of final a C. Well, I don't know what else to say.
Overall the class content is fine and interesting, but try not take it with RRR.

Professor Rosario likes to give hard tests just like Professor Eggert does, but unlike Professor Eggert, his lectures does not prepare you for such kind of hard problems. He goes through simple and easy concepts during his lectures but mentions little about problem-solving skills. To get an A- for this class, you must go to his office hours frequently and ask questions. To get an A for this class, I'm sorry but I believe you have to do many extra practice problems. Moreover, he does not curve the class based on the average but based on what HE THINKS THE AVERAGE SHOULD BE(not bluffing, he mentioned it more than one during class) so you don't really get a lot of curve benefits from hard examinations.

Rosario is actually pretty nice, approachable, and knowledgeable. But if you anger him you will get the hardest final exam of your academic career and wish that Eggert wrote the test instead. Spring 2019 got pwned lol.

TL;DR - do not take CS143 with Rosario. Just not worth it. I made a Bruinwalk account just to post this review in the hope that I can save someone from this class.

Rosario has a massive superiority complex and it seems like he teaches only to get a power trip. He assumes everybody is against him and treats students as such. He is rude and condescending and does not want to help you learn unless you suck up to him at office hours. He cares more about being right and powerful than helping us learn what we joined his class to learn. Tests/specs are unclear, he doesn't like to answer questions, and is borderline abusive on Piazza. A friend of mine was outright cyberbullied by him and others on Piazza, administration did nothing.

I as well as many of my friends have complained to administration about him so I am frankly astonished he is still teaching. This man should not be teaching. Do not think your experience will be different -- do not take this class.