Oracle
集合運算
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基本上可以用下圖表示
Oracle
的幾種集合運算，黃色表示結果集：
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聯合（
Union
）案例：
|
select
1
,
2
from dual
union
select
2
,
3
from dual
|
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完全聯合（
Union All
）案例：
|
select
1
,
2
from dual
unionall
select
1
,
2
from dual
|
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相交
(Intersect)
案例：
|
select
*
from
(
select
1
,
2
from dual
unionall
select
3
,
3
from dual
)
intersect
select
3
,
3
from dual
|
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相減
(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
|
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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
;
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