How to handle the use of federated operations in a database

How to avoid using federated operations in a database
There are three of tables:
User table:

ID Name
1 Kiven
2 Martin
3 Tina

User_class table:

USER_ID class_id
1 1
2 1
3 2

Class table:

ID Name
1 PHP
2 Java
3. Net


I want to output a table that is structured like this:
User_name Class_name
Kiven PHP
Martin PHP
Tina Java


What should I do without a join union query?
Thank you all first.

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Then you just put the data in a table.
But don't say too much redundancy.
------Solution--------------------
The examples in the article are not in accordance with your situation, can not be compared, want to reduce the burden of the database to expand the field
#6的联合查询虽然没用join, but not as efficient as join.

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