一.oracle natural join 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
一.oracle natural join
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');
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)