Oracle internal link + external connection details

Inner join)

An internal join is also called an equivalent join. The returned result set is all the matched data in the two tables, and the unmatched data is discarded. That is to say, in this query, DBMS only returns relevant rows from the source table, that is, the query result table contains two source table rows, which must meet the search conditions in the ON clause. As a comparison, if the rows in the source table do not have corresponding (related) rows in the other table, the row will be filtered out and will not be included in the result table. Internal connections are completed using comparison operators. Intranet connections can be divided into two types.

1. equijoin

Use equal sign (=) to compare the column values of connected columns, and list all columns in the connected table in the query results, including duplicate columns. Figure 9.12 shows a typical equijoin.

Outer right join = Inner join + mismatched tuples in the right table

The value of the missing left table is NULL. Figure 9.20 shows a typical right outer join.

Total Outer Join = Inner join + mismatched tuples in the left table + mismatched tuples in the right table.

The missing attribute values in the Left or Right tables are expressed as NULL. Figure 9.23 shows a typical full outer connection.

Figure 4.2.3.3 all external connections

Lab: