一.Oracle Natural join
<span style="font-size:12px;">create table test_table_A(id number primary key,name varchar(32));create table test_table_B(id number primary key,name varchar(32),des varchar(32));select *from test_table_A;select *from test_table_B;insert into test_table_A(id, name) values(1,'cuiyaonan20 a');insert into test_table_A(id, name) values(2,'cuiyaonan200 a');insert into test_table_A(id, name) values(3,'cuiyaonan2000 a');insert into test_table_A(id, name) values(4,'cuiyaonan2000@163.com a ');insert into test_table_B values(1,'cuiyaonan20 a','des 1');insert into test_table_B values(2,'cuiyaonan200 a','des 2');insert into test_table_B values(3,'cuiyaonan2000 a','des 3');insert into test_table_B values(4,'cuiyaonan20 b','des 1');insert into test_table_B values(5,'cuiyaonan200 b','des 2');insert into test_table_B values(6,'cuiyaonan2000 b','des 3');</span>
?在pl/sql中运行如上实例代码
?
然后执行:
select *from test_table_a natural join test_table_b;
?显示结果为:
?
这就是自连接,A表与B表 如果有同名字段,且字段类型一致,就会整合判断内容是否相等相等就做笛卡尔积.
?
一.Oracle using join
执行如下代码:
select *from test_table_a join test_table_b using(name);
?显示结果为:
?非常明显,using就是相对于natural而言制定了 一列进行匹配(前提条件一致,字段同名,类型一致)