I spent close to 2-months trying to understand this topic from my studies. I spent 30mins with your video and I feel like I have gained relational algebra enlightenment. :) Thank you for doing up this video and teaching it so clearly!
thank u very much madame for an impressive tutorial, am now able to seat for my final db course exam at my college a million thanks once again may God bless u more more more and more......
Wow. These two videos were unbelievably helpful and easy to understand. In less than 40 minutes, you did a better job of covering what took my professor 5 one-hour lectures to cover. When I fill out my course evaluations, I'm going to link these videos. Hopefully my professor can learn from you on how to convey these concepts so efficiently.
These videos are great! In fact, I knew nothing on the subject, and the first video was so good, I actually caught the error she made at 3:58 before reading her correction shortly after. Great job!
This video is proper sick !! I am so much better a at this now and willl flourish when I do my exam on data structures and databases on the 25th of May, 2022 !! :D thank you Jennifer !!
Time 4:00 Couldn't you just add a theta join instead of of a natural join with a project operator. Did you not do this because theta joins are rare? I thought you said otherwise when you explained it to us?
When she does "pairs of colleges in same sate" with the first method, with the cross product, she selected s1 = s2, but don't you also have the Berkley Stanford and Stanford Berkley issue here as well as you did with the natural join?
Yup, she missed that i guess because it was not the final query that she was going to show, it also gets repetitions like "stanford stanford" "berkeley berkeley" i think
But what happens if you have more than 2 colleges that you are looking for pairs of ? She just used Berkeley and Stanford and assigned them to C1 and C2 what i there are 300 colleges do we have to list all of them like that ? (C1, C2...C50... C300)?
I didn't understand the concept of 'natural join' in the Difference operator. The SID is unique in all cases. It cannot be same. So why do we need a 'natural join' to remove duplicate values?
It doesnt allow you to do something you couldnt have done with the opertors introduced before. Its just an easier way to write something however you could have written it before aswell
Siyang Liang Someone correct me if I'm wrong, but you may have to look at previous lectures to understand. That question you are asking is actually not possible in this Student-Apply-School relation because I remember that the sID from the Apply table is the primary key. This means that a constraint of this whole relationship is that students can only apply once to a school.
Ste awoi I think the primary key for Apply is (sID, college, major). A student could apply multiple college. And a student could apply multiple majors for one college. Look at the original apply table.
