oracle的minus返回第一个表中有、第二个表中没有的数据

CREATE TABLE hovertree_union_1 (

id INT,

val VARCHAR(10)

);  

CREATE TABLE hovertree_union_2 (

id INT,

val VARCHAR(10)

);  

INSERT INTO hovertree_union_1 VALUES(1, 'A');

INSERT INTO hovertree_union_1 VALUES(2, 'B');

INSERT INTO hovertree_union_1 VALUES(3, 'C');  

INSERT INTO hovertree_union_2 VALUES(1, 'A');

INSERT INTO hovertree_union_2 VALUES(1, 'A');

INSERT INTO hovertree_union_2 VALUES(2, 'B');

INSERT INTO hovertree_union_2 VALUES(4, 'D');  

SQL> SELECT * FROM hovertree_union_1

2 MINUS

3 SELECT * FROM hovertree_union_2;  

ID VAL

---------- --------------------

3 C  

SQL> SELECT * FROM hovertree_union_2

2 MINUS

3 SELECT * FROM hovertree_union_1;  

ID VAL

---------- --------------------

4 D 

-- 何问起 hovertree.com