Oracle10g中新型層次查詢選項簡介(1)
2024-08-29 13:35:05
供稿：網友
我們可以通過START WITH . . . CONNECT BY . . .子句來實現SQL的 層次查詢，而Oracle 10g 為其添加許多了新的偽列。十多年以來，Oracle SQL 具有依照層次關系進行查詢的功能。例如，你可以指定一個起始條件，然后根據一個或多個連接條件來確定孩子行的內容。舉例來說，現在假設我有一個表，里面記錄了世界上的某些地區，其表結構如下： 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'); 那么我們可以使用START WITH . . . CONNECT BY . . .從句將父級地區與孩子地區連接起來，并將其層次等級顯示出來。 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自從Since Oracle 9i 開始，就可以通過 SYS_CONNECT_BY_PATH 函數實現將從父節點到當前行內容以“path”或者層次元素列表的形式顯示出來。 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，還有其他更多關于層次查詢的新特性 。例如，有的時候用戶更關心的是每個層次分支中等級最低的內容。那么你就可以利用偽列函數CONNECT_BY_ISLEAF來判定當前行是不是葉子。假如是葉子就會在偽列中顯示“1”，假如不是葉子而是一個分支（例如當前內容是其他行的父親）就顯示“0”。下給出了一個關于這個函數使用的例子： 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
自從Since Oracle 9i 開始，就可以通過 SYS_CONNECT_BY_PATH 函數實現將從父節點到當前行內容以“path”或者層次元素列表的形式顯示出來。 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，還有其他更多關于層次查詢的新特性 。例如，有的時候用戶更關心的是每個層次分支中等級最低的內容。那么你就可以利用偽列函數CONNECT_BY_ISLEAF來判定當前行是不是葉子。假如是葉子就會在偽列中顯示“1”，假如不是葉子而是一個分支（例如當前內容是其他行的父親）就顯示“0”。下給出了一個關于這個函數使用的例子：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
