Oracle10g中新型层次查询选项简介(1)

我们可以通过START WITH . . . CONNECT BY . . .子句来实现SQL的层次查询，而Oracle 10g 为其添加许多了新的伪列。十多年以来，Oracle SQL 具有依照层次关系进行查询的功能。例如，你可以指定一个起始条件，然后根据一个或多个连接条件来确定孩子行的内容。举例来说，现在假设我有一个表，里面记录了世界上的某些地区，其表结构如下： create table hier

(

parent varchar2(30),

child varchar2(30)

);

insert into hier values(null,'Asia');

insert into hier values(null,'Australia');

insert into hier values(null,'Europe');

insert into hier values(null,'North America');

insert into hier values('Asia','China');

insert into hier values('Asia','Japan');

insert into hier values('Australia','New South Wales');

insert into hier values('New South Wales','Sydney');

insert into hier values('California','Redwood Shores');

insert into hier values('Canada','Ontario');

insert into hier values('China','Beijing');

insert into hier values('England','London');

insert into hier values('Europe','United Kingdom');

insert into hier values('Japan','Osaka');

insert into hier values('Japan','Tokyo');

insert into hier values('North America','Canada');

insert into hier values('North America','USA');

insert into hier values('Ontario','Ottawa');

insert into hier values('Ontario','Toronto');

insert into hier values('USA','California');

insert into hier values('United Kingdom','England'); 那么我们可以使用START WITH . . . CONNECT BY . . .从句将父级地区与孩子地区连接起来，并将其层次等级显示出来。 column child format a40

select level,lpad(' ',level*3)child child

from hier

start with parent is null

connect by prior child = parent;

LEVEL CHILD

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

1 Asia

2 China

3 Beijing

2 Japan

3 Osaka

3 Tokyo

1 Australia

2 New South Wales

3 Sydney

1 Europe

2 United Kingdom

3 England

4 London

1 North America

2 Canada

3 Ontario

4 Ottawa

4 Toronto

2 USA

3 California

4 Redwood Shores 自从Since Oracle 9i 开始，就可以通过 SYS_CONNECT_BY_PATH 函数实现将从父节点到当前行内容以“path”或者层次元素列表的形式显示出来。如下例所示： column path format a50

select level,sys_connect_by_path(child,'/') path

from hier

start with parent is null

connect by prior child = parent;

LEVEL PATH

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

1 /Asia

2 /Asia/China

3 /Asia/China/Beijing

2 /Asia/Japan

3 /Asia/Japan/Osaka

3 /Asia/Japan/Tokyo

1 /Australia

2 /Australia/New South Wales

3 /Australia/New South Wales/Sydney

1 /Europe

2 /Europe/United Kingdom

3 /Europe/United Kingdom/England

4 /Europe/United Kingdom/England/London

1 /North America

2 /North America/Canada

3 /North America/Canada/Ontario

4 /North America/Canada/Ontario/Ottawa

4 /North America/Canada/Ontario/Toronto

2 /North America/USA

3 /North America/USA/California

4 /North America/USA/California/Redwood Shores 在 Oracle 10g 中，还有其他更多关于层次查询的新特性。例如，有的时候用户更关心的是每个层次分支中等级最低的内容。那么你就可以利用伪列函数CONNECT_BY_ISLEAF来判定当前行是不是叶子。假如是叶子就会在伪列中显示“1”，假如不是叶子而是一个分支（例如当前内容是其他行的父亲）就显示“0”。下给出了一个关于这个函数使用的例子： select connect_by_isleaf,sys_connect_by_path(child,'/') path

from hier

start with parent is null

connect by prior child = parent;

CONNECT_BY_ISLEAF PATH

---------------------------------- 0 /Asia

0 /Asia/China

1 /Asia/China/Beijing

0 /Asia/Japan

1 /Asia/Japan/Osaka

1 /Asia/Japan/Tokyo

0 /Australia

0 /Australia/New South Wales

1 /Australia/New South Wales/Sydney

0 /Europe

0 /Europe/United Kingdom

0 /Europe/United Kingdom/England

1 /Europe/United Kingdom/England/London

0 /North America

0 /North America/Canada

0 /North America/Canada/Ontario

1 /North America/Canada/Ontario/Ottawa

1 /North America/Canada/Ontario/Toronto

0 /North America/USA

0 /North America/USA/California

1 /North America/USA/California/Redwood Shores

自从Since Oracle 9i 开始，就可以通过 SYS_CONNECT_BY_PATH 函数实现将从父节点到当前行内容以“path”或者层次元素列表的形式显示出来。如下例所示： column path format a50

select level,sys_connect_by_path(child,'/') path

from hier

start with parent is null

connect by prior child = parent;

LEVEL PATH

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

1 /Asia

2 /Asia/China

3 /Asia/China/Beijing

2 /Asia/Japan

3 /Asia/Japan/Osaka

3 /Asia/Japan/Tokyo

1 /Australia

2 /Australia/New South Wales

3 /Australia/New South Wales/Sydney

1 /Europe

2 /Europe/United Kingdom

3 /Europe/United Kingdom/England

4 /Europe/United Kingdom/England/London

1 /North America

2 /North America/Canada

3 /North America/Canada/Ontario

4 /North America/Canada/Ontario/Ottawa

4 /North America/Canada/Ontario/Toronto

2 /North America/USA

3 /North America/USA/California

4 /North America/USA/California/Redwood Shores 在 Oracle 10g 中，还有其他更多关于层次查询的新特性。例如，有的时候用户更关心的是每个层次分支中等级最低的内容。那么你就可以利用伪列函数CONNECT_BY_ISLEAF来判定当前行是不是叶子。假如是叶子就会在伪列中显示“1”，假如不是叶子而是一个分支（例如当前内容是其他行的父亲）就显示“0”。下给出了一个关于这个函数使用的例子： select connect_by_isleaf,sys_connect_by_path(child,'/') path

from hier

start with parent is null

connect by prior child = parent;

CONNECT_BY_ISLEAF PATH

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

0 /Asia

0 /Asia/China

1 /Asia/China/Beijing

0 /Asia/Japan

1 /Asia/Japan/Osaka

1 /Asia/Japan/Tokyo

0 /Australia

0 /Australia/New South Wales

1 /Australia/New South Wales/Sydney

0 /Europe

0 /Europe/United Kingdom

0 /Europe/United Kingdom/England

1 /Europe/United Kingdom/England/London

0 /North America

0 /North America/Canada

0 /North America/Canada/Ontario

1 /North America/Canada/Ontario/Ottawa

1 /North America/Canada/Ontario/Toronto