10. MySQL entry summary

1. Connection operations and Set Operations (continued)

Since mysql does not support full join, I can do this:

A B a. id a B a. id B. id

A. First find the left join
B. Right join Detection
C. Use union to combine the two queries
Note: union and union all are combined queries, and union is the set to remove duplicate rows. union all is the complete set to ignore duplicate rows.
In addition, the current MySQL set operations only support union operations, but not intersect and minus.

2. SQL Summary

There are a lot of SQL tutorials on the Internet. Today, let's look at the Learning Website http://www.w3school.com.cn/ SQL /, which is very good (although very simple, after all, SQL is very simple) delivered by Jia GE. Thank you for that.
We recommend that you first systematically learn the SQL statements. The content of the preceding website can be used for query or enhancement. I used to read online content directly and forgot to read it. At that time, I mainly did not have the architecture of SQL learning.