What are the two types of relational operations in the database? What does it mean?

Traditional relational operation of mathematical set and relational operation unique to database.

The database itself is a two-dimensional table, which is equivalent to a collection of mathematics.

Sometimes it is necessary to manipulate two tables, such as finding the same parts in two tables. The operation mechanism is the "intersection" in traditional set operation.

Sometimes the calculation needs to use the table itself, for example, it only needs to display the value of a column in the table, which is the special operation "projection" of the relationship.

You can find the rest of the operation yourself. The basic principle is simple and easy to understand.