Shulou(Shulou.com)06/01 Report--

Oracle left table to practice the level of the way.

I. preparatory work

Oracle connections are divided into:

Left outer join: the left table is unrestricted, the data of the left table is retained, the right table is matched, and the columns in the rows that do not match in the right table are displayed as null.

Right outer connection: there is no restriction on the right table and the data in the right table is retained. Matches the left table, and the columns in the rows that do not match in the left table are displayed as null.

Full external join: there are no restrictions on the left and right tables. That is, the result of the right outer connection is: the data matched by the left and right tables + the data not matched by the left table + the data not matched by the right table.

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