Oracle树查询及相关函数
欢迎进入Oracle社区论坛，与200万技术人员互动交流 >>进入 8.查询一个节点的父节点的的兄弟节点（伯父与叔父）。 Sql代码 WITH tmp AS (SELECT flfl.*, LEVEL lev FROM flfl START WITH sjflid IS NULL CONNECT BY sjflid = PRIOR ID) SELECT b.* FROM tmp b
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8.查询一个节点的父节点的的兄弟节点（伯父与叔父）。
Sql代码
WITH tmp AS
(SELECT flfl.*, LEVEL lev
FROM flfl
START WITH sjflid IS NULL
CONNECT BY sjflid = PRIOR ID)
SELECT b.*
FROM tmp b,
(SELECT *
FROM tmp
WHERE ID = 7004 AND lev = 2) a
WHERE b.lev = 1
UNION ALL
SELECT *
FROM tmp
WHERE sjflid = (SELECT DISTINCT x.ID
FROM tmp x,
tmp y,
(SELECT *
FROM tmp
WHERE ID = 7004 AND lev > 2) z
WHERE y.ID = z.sjflid AND x.ID = y.sjflid);
这里查询分成以下几步。首先，将第7个一样，将全表都使用临时表加上级别；其次，根据级别来判断有几种类型，以上文中举的例子来说，有三种情况：（1）当前节点为顶级节点，即查询出来的lev值为1，那么它没有上级节点，不予考虑。（2）当前节点为2级节点，查询出来的lev值为2，那么就只要保证lev级别为1的就是其上级节点的兄弟节点。（3）其它情况就是3以及以上级别，那么就要选查询出来其上级的上级节点（祖父），再来判断祖父的下级节点都是属于该节点的上级节点的兄弟节点。 最后，就是使用UNION将查询出来的结果进行结合起来，形成结果集。
9.查询一个节点的父节点的同级节点（族叔）。
这个其实跟第7种情况是相同的。
Sql代码
WITH tmp AS
(SELECT a.*, LEVEL lev
FROM flfl a
START WITH a.sjflid IS NULL
CONNECT BY a.sjflid = PRIOR a.ID)
SELECT *
FROM tmp
WHERE lev = (SELECT lev
FROM tmp
WHERE ID = 819394) - 1
只需要做个级别判断就成了。
基本上，常见的查询在里面了，不常见的也有部分了。其中，查询的内容都是节点的基本信息，都是数据表中的基本字段，但是在树查询中还有些特殊需求，是对查询数据进行了处理的，常见的包括列出树路径等。
补充一个概念，对于数据库来说，根节点并不一定是在数据库中设计的顶级节点，对于数据库来说，根节点就是start with开始的地方。
下面列出的是一些与树相关的特殊需求。
10.名称要列出名称全部路径。
这里常见的有两种情况，一种是是从顶级列出，直到当前节点的名称（或者其它属性）；一种是从当前节点列出，直到顶级节点的名称（或其它属性）。举地址为例：国内的习惯是从省开始、到市、到县、到居委会的，而国外的习惯正好相反（老师说的，还没接过国外的邮件，谁能寄个瞅瞅 ）。
从顶部开始：
Sql代码
SELECT SYS_CONNECT_BY_PATH (mc, '/')
FROM flfl
WHERE ID = 6498
START WITH sjflid IS NULL
CONNECT BY sjflid = PRIOR ID;
从当前节点开始：
Sql代码
SELECT SYS_CONNECT_BY_PATH (mc, '/')
FROM flfl
START WITH ID = 6498
CONNECT BY PRIOR sjflid = ID;
在这里我又不得不放个牢骚了。oracle只提供了一个sys_connect_by_path函数，却忘了字符串的连接的顺序。在上面的例子中，第一个SQL是从根节点开始遍历，而第二个SQL是直接找到当前节点，从效率上来说已经是千差万别，更关键的是第一个SQL只能选择一个节点，而第二个SQL却是遍历出了一颗树来。再次PS一下。
sys_connect_by_path函数就是从start with开始的地方开始遍历，并记下其遍历到的节点，start with开始的地方被视为根节点，将遍历到的路径根据函数中的分隔符，组成一个新的字符串，这个功能还是很强大的。
11.列出当前节点的根节点。
在前面说过，根节点就是start with开始的地方。
Sql代码
SELECT CONNECT_BY_ROOT mc, flfl.*
FROM flfl
START WITH ID = 6498
CONNECT BY PRIOR sjflid = ID;
connect_by_root函数用来列的前面，记录的是当前节点的根节点的内容。
12.列出当前节点是否为叶子。
这个比较常见，尤其在动态目录中，在查出的内容是否还有下级节点时，这个函数是很适用的。
Sql代码
SELECT CONNECT_BY_ISLEAF, flfl.*
FROM flfl
START WITH sjflid IS NULL
CONNECT BY sjflid = PRIOR ID;
connect_by_isleaf函数用来判断当前节点是否包含下级节点，如果包含的话，说明不是叶子节点，这里返回0；反之，如果不包含下级节点，这里返回1。
至此，oracle树型查询基本上讲完了，以上的例子中的数据是使用到做过的项目中的数据，因为里面的内容可能不好理解，所以就全部用一些新的例子来进行阐述。以上所有SQL都在本机上测试通过，也都能实现相应的功能，但是并不能保证是解决这类问题的最优方案（如第8条明显写成存储过程会更好），如果谁有更好的解决方案、或者有关oracle树查询的任何问题，欢迎留言讨论，以上的SQL有什么问题也欢迎大家留言批评。
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