Oracle
集合运算
基本上可以用下图表示
Oracle
的几种集合运算，黄色表示结果集：
联合（
Union
）案例：
|
select
1
,
2
from dual
union
select
2
,
3
from dual
|
完全联合（
Union All
）案例：
|
select
1
,
2
from dual
unionall
select
1
,
2
from dual
|
相交
(Intersect)
案例：
|
select
*
from
(
select
1
,
2
from dual
unionall
select
3
,
3
from dual
)
intersect
select
3
,
3
from dual
|
相减
(minus)
案例：
|
select
a,b
from
(
select
1
as a,
2
as b
from dual
unionall
select
3
as a,
3
as b
from dual
)
MINUS
select
3
as a,
3
as b
from dual
|
Union
排序只能放在最后
|
COLUMN
a_dummy NOPRINT
SELECT
'sing'
AS "My dream",
3
a
_dummy
FROM dual
UNION
SELECT
'I''d like to teach'
,
1
FROM dual
UNION
SELECT
'the world to'
,
2
FROM dual
ORDERBY
2
;
|