Oracle树反向查询的优化(转载)
Selecting a 'pruned tree' with selected nodes and all their ancestors – Hierarchical SQL Queries and Bottom-Up Trees
Hierarchical queries return data in a tree like structure. The query is performed by walking the tree that is made up of parents and children, each non-root-node linked to a parent node. A common example of a hierarchical query is the one involving Employees who are linked to each other through the Manager reference.
I was recently facing a situation where I wanted to retrieve a number of nodes from a tree-like data structure, based on certain criteria. I wanted to present the resulting nodes again in a tree like fashion. However, if a child node was selected and its parent or other ancestors were not, I could not set up the tree structure to present the selected nodes in. So I have to make sure that along with certain specific nodes, also all their ancestors nodes are returned in order to restore the tree.
In this article, I will demonstrate several ways of creating such a query, one that returns selected nodes and their ancestors, given a specific hierarchical relation between records. The solutions I show make use of Oracle 9i features – the sys_connect_by_path operator and the combination of hierarchical queries and joins in a single query, which was not allowed prior to 9i.
What do we want to achieve?
We start from the classical EMP table. This table has three columns of interest: EMPNO (primary key), ENAME (display label) and MGR (self referencing foreign key). We use the connection between MGR and EMPNO to build the hierarchy. The simplest query to retrieve the EMP “tree” is this one:
select lpad('+',3*(level-1))||ename||'('||empno||')'Employeefrom emp
connect
by prior empno = mgr
start
with mgr isnull/
Note how we added the lpad function to create indentation for the non-root nodes in our tree. We use the pseudo-column LEVEL that indicates the level of nesting (or the number of ancestors) for any node in the tree. The result looks like this:
EMPLOYEE
----------------------------------
KING(7839)+JONES(7566)+SCOTT(7788)+ADAMS(7876)+FORD(7902)+SMITH(7369)+TURNER(7844)+MARTIN(7654)+BLAKE(7698)+ALLEN(7499)+WARD(7521)+JAMES(7900)+CLARK(7782)+MILLER(7934)14 rows selected.
This query could be executed as far back as Oracle 7 (or perhaps even earlier). In Oracle 9i, two knew features were introduced for hierarchical queries: the ability to join with other tables inside an hierarchical query and the operator SYS_CONNECT_BY_PATH. The latter returns for any node in the tree the concattenation of a certain expression for all nodes from the current node through all its ancestors all the way up to the root node. For example:
select lpad('+',3*(level-1))||ename||' ('||dname||') '||sys_connect_by_path(job,'/')Employeefrom emp
, dept
where emp.deptno = dept.deptno
connect
by prior empno = mgr
start
with mgr isnull
Here we request the JOB value for each node and all its ancestors. The Job values are separated by the ‘/’ sign:
EMPLOYEE
-------------------------------------------------------------------------------------
KING (ACCOUNTING)/PRESIDENT
+JONES (RESEARCH)/PRESIDENT/ANALYST
+SCOTT (RESEARCH)/PRESIDENT/ANALYST/ANALYST
+ADAMS (RESEARCH)/PRESIDENT/ANALYST/ANALYST/CLERK
+FORD (RESEARCH)/PRESIDENT/ANALYST/ANALYST
+SMITH (RESEARCH)/PRESIDENT/ANALYST/ANALYST/CLERK
+TURNER (SALES)/PRESIDENT/ANALYST/ANALYST/CLERK/SALESMAN
+MARTIN (SALES)/PRESIDENT/ANALYST/ANALYST/CLERK/SALESMAN/ACCOUNTNT
+BLAKE (SALES)/PRESIDENT/MANAGER
+ALLEN (SALES)/PRESIDENT/MANAGER/SALESMAN
+WARD (SALES)/PRESIDENT/MANAGER/SALESMAN
+JAMES (SALES)/PRESIDENT/MANAGER/CLERK
+CLARK (ACCOUNTING)/PRESIDENT/MANAGER
+MILLER (ACCOUNTING)/PRESIDENT/MANAGER/CLERK
Now returning to the job at hand. I want to be able to select from the tree-like structure all nodes that satisfy certain conditions, for example the requirement that the SAL is greater than 3000 or the ENAME contains an ‘I’. However, I want to represent the result in a tree, with all manager-ancestors for each selected employee. Clearly simply adding a where clause of where ename like '%I%'
will not do the trick here:
select lpad('+',3*(level-1))||ename||'('||empno||')'Employeefrom emp
where ename like '%I%'
connect
by prior empno = mgr
start
with mgr isnull/
The result is clearly not what we intended:
EMPLOYEE
----------------------------
KING(7839)+SMITH(7369)+MARTIN(7654)+MILLER(7934)
We lack the managers of SMITH, MARTIN and MILLER – because obviously their names do not include an ‘I’. So what to do instead?
We need a way to include not only the nodes that directly satisfy the search condition, but also their ancestors. Here we can make use of the SYS_CONNECT_BY_PATH function. We can for example ask each selected node for its SYS_CONNECT_BY_PATH for the EMPNO column. This gives us not only the Employees that satisfy the criteria, but also a list of the EMPNO values for their ancestors in the tree:
select ename
, empno
, sys_connect_by_path(empno,'.')||'.' scbp
from emp
connect
by prior empno = mgr
start
with mgr isnull/
ENAME EMPNO SCBP
----------------------------------------------------
KING 7839.7839.
JONES 7566.7839.7566.
SCOTT 7788.7839.7566.7788.
ADAMS 7876.7839.7566.7788.7876.
FORD 7902.7839.7566.7902.
SMITH 7369.7839.7566.7902.7369.
TURNER 7844.7839.7566.7902.7369.7844.
MARTIN 7654.7839.7566.7902.7369.7844.7654.
BLAKE 7698.7839.7698.
ALLEN 7499.7839.7698.7499.
WARD 7521.7839.7698.7521.
JAMES 7900.7839.7698.7900.
CLARK 7782.7839.7782.
MILLER 7934.7839.7782.7934.
We can make use of this approach in the following way:
with tree as(select ename
, empno
, sys_connect_by_path(empno,'.')||'.' scbp
from emp
connect
by prior empno = mgr
start
with mgr isnull)select distinct
emp.empno
, emp.ename
, emp.mgr
from tree
, emp
where instr('.'||tree.scbp,emp.empno||'.')>0--select any employee whose empno is part of the path from the selected tree-nodes all the way to the top
and tree.ename like '%I%'--from the entire tree, only select those nodes that satisfy the search requirements
/
First we build the tree – with all the nodes – in the inline view ‘tree’. Then we select from the tree only the nodes that satisfy the search condition. Last we join these selected tree-nodes with table EMP using the condition instr('.'||tree.scbp,emp.empno||'.') > 0
. This specifies that if the SYS_CONNECT_BY_PATH on EMPNO for one of the selected tree-nodes includes the primary key EMPNO of a record in EMP, that record should be includes, as it is either a directly selected tree node (with an I in the ENAME) or one of the ancestors of such a node. The result:
EMPNO ENAME MGR
------------------------------7369 SMITH 79027566 JONES 78397654 MARTIN 78447782 CLARK 78397839 KING
7844 TURNER 73697902 FORD 75667934 MILLER 77828 rows selected.
Now we would like to present this search result in a tree-structure. Using this record set, which we know to include all ancestor nodes from the selected nodes to the root, it should be simple to create the tree again:
with tree as(select ename
, empno
, sys_connect_by_path(empno,'.')||'.' scbp
from emp
connect
by prior empno = mgr
start
with mgr isnull), selected_tree_nodes as(select distinct
emp.empno
, emp.ename
, emp.mgr
from tree
, emp
where instr('.'||tree.scbp,emp.empno||'.')>0--select any employee whose empno is part of the path from the selected tree-nodes all the way to the top
and tree.ename like '%I%'--from the entire tree, only select those nodes that satisfy the search requirements
)select lpad(ename,level*3+10)||' ('||empno||')' emp_node --finally build a tree from the subset of nodes that were returned
from selected_tree_nodes
connect
by PRIOR empno = mgr
start
with mgr isnull/
The resulting tree looks like this:
EMP_NODE
-----------------------------------
KING (7839)
JONES (7566)
FORD (7902)
SMITH (7369)
TURNER (7844)
MARTIN (7654)
CLARK (7782)
MILLER (7934)8 rows selected.
Alternative approach: Bottom Up Tree
Instead of building the entire tree of employees, starting from all root-nodes and traversing down through all nodes, including nodes and entire sub-branches that do not qualify, is perhaps somewhat overdoing it. Could there not be a more direct approach? What if we start by selecting all nodes that qualify and then build the tree from these nodes? If we need only a few nodes from just a few branches of the tree, would this not be much cheaper? Well, it probably would be. Let’s see how to do this.
select e1.*, e2.empno marker
from emp e1
left outer join
(select empno
from emp
where ename like '%I%') e2 -- find all empnos of employees that satisfy the search requirement
on (e1.empno = e2.empno)/
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO MARKER
----------------------------------------------------------------------------------------7369 SMITH CLERK 790217-DEC-808002073697654 MARTIN ACCOUNTNT 784428-SEP-81125014003076547839 KING PRESIDENT 17-NOV-8150001078397934 MILLER CLERK 778223-JAN-8213001079347844 TURNER SALESMAN 736908-SEP-8115000307782 CLARK MANAGER 783909-JUN-812450107521 WARD SALESMAN 769822-FEB-811250500307788 SCOTT ANALYST 756609-DEC-823000207698 BLAKE MANAGER 783901-MAY-812850307566 JONES ANALYST 783902-APR-812975207499 ALLEN SALESMAN 769820-FEB-811600300307902 FORD ANALYST 756603-DEC-813000207876 ADAMS CLERK 778812-JAN-831100207900 JAMES CLERK 769803-DEC-8195030
Here we selected all EMP records, and for each record we have determined whether or not it is one of the selected nodes; this is indicated through the MARKER column. Next we are going to use this set to build a tree, starting from all the nodes that have a value for their marker:
with emps as-- all employees with a marker column for those that satisfy the search requirement
(select e1.*, e2.empno marker
from emp e1
left outer join
(select empno
from emp
where ename like '%I%') e2 -- find all empnos of employees that satisfy the search requirement
on (e1.empno = e2.empno))select distinct
ename
, empno
from emps
connect
by PRIOR mgr=empno -- note that the connect by condition is exactly the reverse of the one we used earlier; it reflects the fact that we build the tree from the bottom upwards, linking records to the MGR reference of the prior node
start
with marker isnotnull/
The result looks familiar, as it should:
ENAME EMPNO
--------------------
CLARK 7782
FORD 7902
JONES 7566
KING 7839
MARTIN 7654
MILLER 7934
SMITH 7369
TURNER 78448 rows selected.
A slightly more compact alternative for this query is the following – it can be used whenever the condition to select the nodes is relatively simple and does not require a subquery:
with emps as-- all employees with a marker column for those that satisfy the search requirement
(select e1.*,casewhen ename like '%I%'then'X'end marker
from emp e1
)select distinct
ename
, empno
from emps
connect
by PRIOR mgr=empno
start
with marker isnotnull/
Finally, building a tree from the query result - showing all employees whose names contain an 'I'with all their managerial burden,isdone like this:
with emps as-- all employees with a marker column for those that satisfy the search requirement
(select e1.*,casewhen ename like '%I%'then'X'end marker
from emp e1
), tree_nodes as(select distinct
ename
, empno
, mgr
from emps
connect
by PRIOR mgr=empno
start
with marker isnotnull)select lpad(ename, level *4)from tree_nodes
connect by prior empno = mgr
start with mgr isnull/
The result, again,is familiar:
LPAD(ENAME,LEVEL*4)------------------------------
KING
CLARK
MILLER
JONES
FORD
SMITH
TURNER
MARTIN 8 rows selected.
Note: if for some reason the WITH clause cannot be used – and it seems that for example Oracle ADF Business Components does not like it – you can rewrite the above queries using plain In Line views:
select distinct
ename
, empno
from(select e1.*, e2.empno marker
from emp e1
left outer join
(select empno
from emp
where ename like '%I%') e2 -- find all empnos of employees that satisfy the search requirement
on (e1.empno = e2.empno))
connect
by PRIOR mgr=empno
start
with marker isnotnull
and the last one:
select lpad(ename, level *4)from(select distinct
ename
, empno
, mgr
from(select e1.*, e2.empno marker
from emp e1
left outer join
(select empno
from emp
where ename like '%I%') e2 -- find all empnos of employees that satisfy the search requirement
on (e1.empno = e2.empno))
connect
by PRIOR mgr=empno
start
with marker isnotnull)
connect by prior empno = mgr
start with mgr isnull
Oracle树反向查询的优化(转载)的更多相关文章
- Oracle的分页查询语句优化
Oracle的分页查询语句基本上可以按照本文给出的格式来进行套用. (一) 分页查询格式: SELECT * FROM ( SELECT A.*, ROWNUM RN FROM (SELECT ...
- oracle 树状查询
做树状查询的时候,oracle有自己的优势,一条sql语句就可以搞定,而mysql这种数据库就只能用递归了... 递归的项目实例: //递归取到栏目路径 public List getTreeList ...
- (转载)Oracle 树操作(select…start with…connect by…prior)
转载地址:https://www.cnblogs.com/linjiqin/p/3152674.html 备注:如有侵权,请立即联系删除. oracle树查询的最重要的就是select…start w ...
- Oracle树查询及相关函数
Oracle树查询的最重要的就是select...start with... connect by ...prior 语法了.依托于该语法,我们可以将一个表形结构的中以树的顺序列出来.在下面列述了Or ...
- oracle树操作(select start with connect by prior)
oracle中的递归查询可以使用:select .. start with .. connect by .. prior 下面将会讲述oracle中树形查询的常用方式,只涉及到一张表. 一. 建表语句 ...
- IT该忍者神龟Oracle 树操作(select…start with…connect by…prior)
oracle树查询的最重要的就是select-start with-connect by-prior语法了.依托于该语法.我们能够将一个表形结构的以树的顺序列出来. 在以下列述了oracle中树型查询 ...
- Oracle 树操作(select…start with…connect by…prior)
摘自:http://www.cnblogs.com/linjiqin/archive/2013/06/24/3152674.html oracle树查询的最重要的就是select…start with ...
- [转]Oracle 树操作(select…start with…connect by…prior)
转自http://www.cnblogs.com/linjiqin/archive/2013/06/24/3152674.html Oracle 树操作(select-start with-conne ...
- Oracle学习之Oracle 树操作(select…start with…connect by…prior)
转自:http://www.cnblogs.com/linjiqin/archive/2013/06/24/3152674.html oracle树查询的最重要的就是select…start with ...
随机推荐
- LOL是什么意思? - 已解决 - 搜狗问问
LOL是什么意思? - 已解决 - 搜狗问问 N A T S U . |分类:QQ工具栏 2009-05-04 LOL是什么意思? 满意答案 Shim Nyong 19级 2009-05-04 LOL ...
- Oracle 基础查询知识点
1.Oracle 别名 如果非固定格式的列名可以如此 select last_name as name from employees 如果想显示固定格式的别名的话,则别名必须使用"" ...
- jQuery实现拖动布局并将排序结果保存到数据库
很多网站的拖动布局的例子都是采用浏览器的COOKIE来记录用户拖动模块的位置,也就是说拖动后各模块的排序位置信息是记录在客户端的cookie里的.当用户清空客户端的cookie或浏览器的cookie过 ...
- node.js(七) 子进程 child_process模块
众所周知node.js是基于单线程模型架构,这样的设计可以带来高效的CPU利用率,但是无法却利用多个核心的CPU,为了解决这个问题,node.js提供了child_process模块,通过多进程来实现 ...
- 在.NET下学习Extjs(第四个案例 Extjs扩展的原理)
1.构建如下代码 <!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml"> <head& ...
- 关于VFP9.0备注字段(memo)插入编辑问题
最近在做项目 用VFP9.0这个比较古老的数据库,有个问题一直纠结我很久.就是memo这个备注字段,你在insert 的时候只要插入的字符串数据超过64K的时候就会出错. 之后我一直在找原因原来是备注 ...
- OC语法1——OC概述
Object-C简介: OC,即Object-C,iOS开发的核心语言.它是基于C语言的,在C的基础上做了面向对象的封装,所以OC是面向对象的语言.同时也因此OC是兼容C的,也就是说在iOS开发中,可 ...
- APP分享抓取网页图片
var getShareImages = { defaultimg:"defaultimg.png", _allImgs:null, init:function(){ getSha ...
- firefox 自写扩展改版,总结
自己写的扩展,油猴功能,进一步改进,增加了许多操作.原来只是在13以下版本下面能用,主要是在13版本下面chrome代码和page下面代码能够直接互调,13版本以后就不可以了,最近考虑到新版Firef ...
- lua学习笔记1
lua中调用c的函数 #include <stdio.h> #include <string.h> #ifdef __cplusplus extern "C" ...