Oracle's four types of connections: left outer connection, right outer connection, inner connection, and all outer connection

Oracle's four types of connections: left outer connection, right outer connection, inner connection, and all outer connection

Oracle outer join includes the following:

Left outer join (no restriction on the left table) left [outer] join, a. key = B. key (+)

Right outer join (no restriction on the right table) righ [outer] join, a. key (+) = B. key

Full outer join (left and right tables are not restricted) full [outer] join

Internal join (left and right table public department) [inner] join

Cartesian cross join

You can also use "(+)" for external connections. Notes for using (+:

The (+) operator can only appear in the WHERE clause and cannot be used with the outer join syntax.

When an external join is executed using the (+) operator, if the WHERE clause contains multiple conditions, the (+) operator must be included in all conditions. ?

The (+) operator is only applicable to columns and cannot be used in expressions.

The (+) operator cannot be used with the OR and IN operators.

The (+) operator can only be used to implement left Outer Join and right outer join, but not to implement full outer join.

This number can be understood as follows: + indicates the supplement, that is, which table has a plus sign, and this table is a matching table. If the plus sign is written in the right table, the left table is all displayed, so it is left join.