Rather than feeling like you understood and explained everything in the lecture, I often felt like you were just reading the text in some items. There were a lot of typos, and some of the answers to previous exam questions were wrong. In the case of previous exam questions, there are many materials with clear answers, but since you wrote completely different answers and moved on naturally, my trust in the lecture dropped. I also didn't understand why using the NVL function was the correct answer for question 14, so I looked it up in other past exam questions and found that the wording of the question was missing. (Lecture problem) MGR column value is printed as "9999" (Actual problem) If MGR column value is NULL, it is printed as "9999" I wonder if it is meaningful to teach incorrect content in a certification exam lecture where the correct and incorrect answers are clearly divided.