DB2 INTERSECT、EXCEPT、UNION集合操作测试
说明：DB2支持三种集合操作INTERSECT（交集）、EXCEPT（差集）、UNION（合集），在ORACLE等数据库里面也有类似的操作，但是细微的地方可能有些差别，现在专门测试一下，以求准确！玩数据千万要细心啊，否则会带来难以意料的结果，呵呵！
测试环境：
DROP TABLE AA_WEEK;
CREATE TABLE AA_WEEK(
CODE SMALLINT NOT NULL,
EN_NAME VARCHAR(20) NOT NULL,
ABB VARCHAR(20),
CONSTRAINT P_AA_WEEK_CODE PRIMARY KEY (CODE)
);
COMMENT ON TABLE AA_WEEK IS
‘星期’;
COMMENT ON AA_WEEK
(CODE IS ‘星期代码’,
EN_NAME IS ‘英文星期名’,
ABB IS ‘英文缩写’
);
INSERT INTO AA_WEEK VALUES
(1,‘Monday’,‘Mon’),
(2,‘Tuesday’,‘Tues’),
(3,‘Wednesday’,‘Wed’),
(4,‘Thursday’,‘Thurs’),
(5,‘Friday’,‘Friday’),
(6,‘Saturday’,‘Sat’),
(7,‘Sunday’,‘Sun’);
COMMIT;
查询一把，看看所有数据：
SELECT * FROM AA_WEEK;
±-----±----------±-------+
| CODE | EN_NAME | ABB |
±-----±----------±-------+
| 1 | Monday | Mon |
| 2 | Tuesday | Tues |
| 3 | Wednesday | Wed |
| 4 | Thursday | Thurs |
| 5 | Friday | Friday |
| 6 | Saturday | Sat |
| 7 | Sunday | Sun |
±-----±----------±-------+
一、交集运算：INTERSECT、INTERSECT ALL
– 求交集：A交B
SELECT * FROM AA_WEEK X WHERE X.CODE IN (1,2,3) – 集合A
INTERSECT – 集合B
SELECT * FROM AA_WEEK X WHERE X.CODE IN (2,3,4);
2 ‘Tuesday’ ‘Tues’
3 ‘Wednesday’ ‘Wed’
说明：INTERSECT和INTERSECT ALL是等效的。
二、差集运算：EXCEPT、EXCEPT ALL
– 求差集：A减B
SELECT * FROM AA_WEEK X WHERE X.CODE IN (1,2,3) – 集合A
EXCEPT – 集合B
SELECT * FROM AA_WEEK w WHERE w.CODE IN (2,3,4);
说明：EXCEPT和EXCEPT ALL是等效的。
1 ‘Monday’ ‘Mon’
三、合集运算：UNION、UNION ALL
– 求合集：A+B（不消除重复行）
SELECT * FROM AA_WEEK X WHERE X.CODE IN (1,2,3) – 集合A
UNION ALL – 集合B
SELECT * FROM AA_WEEK X WHERE X.CODE IN (2,3,4);
2 ‘Tuesday’ ‘Tues’
3 ‘Wednesday’ ‘Wed’
4 ‘Thursday’ ‘Thurs’
1 ‘Monday’ ‘Mon’
2 ‘Tuesday’ ‘Tues’
3 ‘Wednesday’ ‘Wed’
– 求合集：A+B（消除重复行）
SELECT * FROM AA_WEEK X WHERE X.CODE IN (1,2,3) – 集合A
UNION – 集合B
SELECT * FROM AA_WEEK X WHERE X.CODE IN (2,3,4);
1 ‘Monday’ ‘Mon’
4 ‘Thursday’ ‘Thurs’
2 ‘Tuesday’ ‘Tues’
3 ‘Wednesday’ ‘Wed’
说明：UNION和UNION ALL是不同的。UNION消除重复行记录，UNION ALL不消除重复行记录。
