Internal joins of databases, outer joins __ database

database of internal and external links reproduced Web site: http://www.cnblogs.com/younes/archive/2010/07/12/1776046.html

There are now two tables: Customers and Orders

Customer table,

Orders table,

Normal query,

Left outer join query,

Right outer join query,

Inner JOIN query,

Description

1 The normal Query method is the default for the inner join.

2 The INNER JOIN query displays only two columns of the query criteria that exist in two tables. If the query condition is customers.cust_id = orders.cust_id, the ID 2002 of a customer exists only in the Customers table and not in the Orders table. So do not show.

3 outer join query, when using the outer join syntax, you must use the right or left keyword, which points to left table as the base table, and vice versa. The Left keyword indicates that as long as cust_id appears in the left-hand table, the result must contain this cust_id, even if the cust_id does not appear in the right table.