A brief discussion on the connection mode of table (inner connection, outer connection, cross connection, self-connection)

Preface

The connection types are divided into three categories: inner connection , outer connection , Cross connection . Inner joins use the INNER join keyword, INNER join matches a common value in two tables, and only rows that meet the join condition are used to build the result set, INNER Join is the default join type and can only be overridden with the join keyword.

There are three types of outer joins: the leftOUTER join, the rightOUTER join and the full OUTER join, and the inner join are different, left OUTER The join also returns rows that do not match the first table , and the right OUTER join also returns rows that do not match the second table , and the full OUTER join returns rows that do not match the left table and the left table .

There is also a cross join (ACROSS join), which returns the Cartesian product, but this is seldom used in the project and has no practical significance.

Internal Connection

　

A brief discussion on the connection mode of table (inner connection, outer connection, cross connection, self-connection)