In an inner join, only those data rows that have matching data in the join table are returned.

Outer join means adding an empty row to the joined table to match the data, but not the row.

For example, if you query the department to which an employee belongs, the president does not belong to any department (the boss does not belong to any department, and the dname item is empty).

Select e. employee name, D. department name data name

From employee e department d

Where, department number = department number (+)

ename DNA name

——————————

Sam sales

Tom accounting

king