Misunderstanding Analysis on SQL nesting

I used to think that when SQL statements are nested, the constraints of nested queries are irrelevant to those of outer layers.

I used to think that when SQL statements are nested, the constraints of nested queries are irrelevant to those of outer layers.

Today I found this conclusion wrong. However, for ease of understanding, I still do not recommend that you confuse the constraints with those outside when you are not familiar with SQL statements. In terms of readability, it can be assumed that it is irrelevant. Due to the time, I will not explain the specific differences in words. I will show you the running results. By thinking about this problem, I suddenly understood some confusions of the previous exist statement, if you are free, try again. 12 if you are interested, you can think about it yourself or communicate with me. I welcome you to discuss some issues with me. I am also learning and improving with you.
Make by Liu runjia