外连接实验(先过滤后连接与先连接后过滤)

[@more@]

Connected to Oracle Database 企业版发布版本...并运行版本...
连接至 Oracle Database 运营版本...执行版本...
--------建立测试表 WT-Test-Table-Base（WT-Basic）
创建测试表 named "wt-test-basic"

Table dropped

SQL> drop TABLE wt2;

Table dropped

SQL> create TABLE wt1(x NUMBER, y NUMBER);

Table created

SQL>
SQL> INSERT INTO wt1 SELECT 1,11 from dual;

1 row inserted
SQL> INSERT INTO wt1 SELECT 2,22 from dual;

1 row inserted

SQL> commit;

Commit complete

SQL> create TABLE wt2(x NUMber,y NUMBER ,z NUMBER);

Table created

SQL>
SQL> INSERT INTO wt2 SELECT 1,NULL,3 from dual;