Misunderstanding of SQL nested
Today I found that this conclusion was wrong.But in order to facilitate understanding, I still do not recommend that you confuse the inner constraints with the outer constraints when you are not familiar with SQL statements.In terms of readability, it can be assumed that it doesn't matter.
Due to the time factor, I will not explain the specific differences in text.I will show you a screenshot of the running results.After thinking about this problem, I immediately understand some of the confusion of the previous exist statement, everyone Try to figure it out when you have time.
Screenshot 1
Screenshot 2
Anyone who is interested can figure it out for yourself or communicate with me.I very much welcome everyone to discuss some issues with me, and I am also learning and progressing with you.
make by Liu Runjia
make by Liu Runjia
Tags
Technical otaku
Sought technology together
0 Comments