Difference between Oracle Outer Join and self-join Oracle Outer Join left and right. Full join

This connection is often used in early query statements, which is a small problem. Therefore, I checked the information and summarized it as follows:

 

External connections are easier to understand,
A. It is generally used in some classification codes. For example, if you have an employee information table, the position information isCodeAnd the meaning of this Code is described in the position table.
B. Classified information storage. For example, in the preceding employee information table, the monthly salary of the employee information table is collected in a table. At this time, external join is required for table Association.
The field associated with the outer join is generally the same or similar to the data type and name. You can write from a left join B on A. ID = B. ID

The self-connection is special and generally reflects the relationship between superiors and subordinates. For example, in the employee information table, there is a field: Superior leadership. The superior corresponding to this field is actually an employee, this employee information is searched through self-connection.
Self-join generally requires a special field in the Table. During connection, note that, for example, from a tab1 left join a tab2 on tab1.up _ id = tab2.id

 

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