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这个函数使用之前必须先建立一个树，否则无用
sys_connect_by_path(字段名, 2个字段之间的连接符号)，注意这里的连接符号不要使用逗号，oracle会报错，如果一定要用，可以使用replace替换一下，方法如下 REPLACE(字段名,原字符,',')。
树: start with 条件1 connect by prior 条件2
条件1如 子=XX (或父=XX)
条件2 若: 子-->根(倒树) 则为 connect by 子 = prior 根
若 根--> 子(正树) 则 connect 根 = prior 子
-- 子全部显示 根-->子 level代表级别 with tmp_a as ( select '1' a,'0' p from dual union all select '2','1' from dual union all select '3','1' from dual union all select '4','3' from dual union all select '5','2' from dual union all select '6','5' from dual ) select a,p,sys_connect_by_path(a,'--'),level from tmp_a start with a = 1 connect by p = prior a -- 2和2的所有下级去掉 根-->子 (开始就要去掉)
with tmp_a as ( select '1' a,'0' p from dual union all select '2','1' from dual union all select '3','1' from dual union all select '4','3' from dual union all select '5','2' from dual union all select '6','5' from dual ) select a,p,sys_connect_by_path(a,'--') from tmp_a start with p = 1 and a <> '2' connect by p = prior a -- 2的所有下级都去掉 根-->子 (connect 时去掉)
with tmp_a as ( select '1' a,'0' p from dual union all select '2','1' from dual union all select '3','1' from dual union all select '4','3' from dual union all select '5','2' from dual union all select '6','5' from dual ) select a,p,sys_connect_by_path(a,'--') from tmp_a start with a = 1 connect by p = prior a and p <> '2' --去掉2的分枝 -- 2的下一级去掉 根-->子 (where 中去掉)
with tmp_a as ( select '1' a,'0' p from dual union all select '2','1' from dual union all select '3','1' from dual union all select '4','3' from dual union all select '5','2' from dual union all select '6','5' from dual ) select a,p,sys_connect_by_path(a,'--') from tmp_a where p <> '2' -- 2 start with a = 1 connect by p = prior a --显示最长的 根-->子
with tmp_tab as ( select '中国' s,null b from dual union all select '广东' s,'中国' b from dual union all select '湖南' s,'中国' b from dual union all select '衡阳' s,'湖南' b from dual union all select '广州' s,'广东' b from dual union all select '衡东' s,'衡阳' b from dual ) select max(sys_connect_by_path(s,'/')) from tmp_tab start with s = '湖南' connect by prior s = b -- -- 构造树 start with rn1 = 1 connect by rn - 1 = prior rn
with tmp_tab as ( select '1' tno,'n1' flag from dual union all select '1' tno,'n2' flag from dual union all select '1' tno,'n3' flag from dual union all select '2' tno,'t1' flag from dual union all select '2' tno,'t3' flag from dual union all select '3' tno,'f1' flag from dual union all select '3' tno,'f2' flag from dual union all select '3' tno,'f3' flag from dual union all select '3' tno,'f4' flag from dual ) select a.*,sys_connect_by_path(a.flag,'--') from ( select tno,flag,tno+row_number() over (order by tno) rn, row_number() over (partition by tno order by tno) rn1 from tmp_tab ) a start with rn1 = 1 connect by rn - 1 = prior rn -- 构造树 ，并取每组最大值，并去掉最前面的 -- 符号 , 并把 -- 换成 , (可用ltrim或substr(str,3))
with tmp_tab as ( select '1' tno,'n1' flag from dual union all select '1' tno,'n2' flag from dual union all select '1' tno,'n3' flag from dual union all select '2' tno,'t1' flag from dual union all select '2' tno,'t3' flag from dual union all select '3' tno,'f1' flag from dual union all select '3' tno,'f2' flag from dual union all select '3' tno,'f3' flag from dual union all select '3' tno,'f4' flag from dual ) select tno,replace(ltrim(max(sys_connect_by_path(a.flag,'--')),'--'),'--',',') from ( select tno,flag, DENSE_RANK() OVER(ORDER BY tno)+row_number() over (order by tno) rn,
row_number() over (partition by tno order by tno) rn1 from tmp_tab ) a start with rn1 = 1 connect by rn - 1 = prior rn group by tno SYS_CONNECT_BY_PATH 函数
SYS_CONNECT_BY_PATH 和几个伪列CONNECT_BY_ROOT,CONNECT_BY_LEAF,CONNECT_BY_ISCYCLE SYS_CONNECT_BY_PATH 函数
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来判断当前行是不是叶子。如 果是叶子就会在伪列中显示“1”，如果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 在Oracle 10g 中还有一个新操作——CONNECT_BY_ROOT。 它用在列名之前用于返回当前层的根节点。如下面的例子，我可以显示出层次结构表中当前行数据所对应的最高等级节点的内容。
select connect_by_root child,sys_connect_by_path(child,"/") path
from hier start with parent is null connect by prior child = parent; CONNECT_BY_ROOT PATH
------------------------------ -------- Asia /Asia Asia /Asia/China Asia /Asia/China/Beijing Asia /Asia/Japan Asia /Asia/Japan/Osaka Asia /Asia/Japan/Tokyo Australia /Australia Australia /Australia/New South Wales Australia /Australia/New South Wales/Sydney Europe /Europe Europe /Europe/United Kingdom Europe /Europe/United Kingdom/England Europe /Europe/United Kingdom/England/London North America /North America North America /North America/Canada North America /North America/Canada/Ontario North America /North America/Canada/Ontario/Ottawa North America /North America/Canada/Ontario/Toronto North America /North America/USA North America /North America/USA/California North America /North America/USA/California/Redwood Shores 在Oracle 10g 之前的版本中，如果在你的树中出现了环状循环（如一个孩子节点引用一个父亲节点），Oracle 就会报出一个错误提示：“ ORA-01436: CONNECT BY loop in user data”。如果不删掉对父亲的引用就无法执行查询操作。而在 Oracle 10g 中，只要指定“NOCYCLE”就可以进行任意的查询操作。与这个关键字相关的还有一个伪列——CONNECT_BY_ISCYCLE， 如果在当前行中引用了某个父亲节点的内容并在树中出现了循环，那么该行的伪列中就会显示“1”，否则就显示“0”。如下例所示：
create table hier2
( parent number, child number ); insert into hier2 values(null,1);
insert into hier2 values(1,2); insert into hier2 values(2,3); insert into hier2 values(3,1); select connect_by_iscycle,sys_connect_by_path(child,"/") path
from hier2 start with parent is null connect by nocycle prior child = parent; CONNECT_BY_ISCYCLE PATH
------------------ ------- 0 /1 0 /1/2 1 /1/2/3 本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/lky5387/archive/2009/12/09/4972310.aspx |
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