Oracle选择连续的子行。Oracle首先选择步骤2中返回的行的子行,然后选择这些子行的子行,依此类推。Oracle总是通过对当前父行计算CONNECT by条件来选择子行。 4、如果查询中包含WHERE子句但不包含join,那么Oracle会从层次结构中消除所有不满足WHERE子句condition的所有行。 5、Oracle按照图9-1所示的顺序返回行。在图中,ch...
接下来,Oracle将使用上面计算获取的信息形成层级: Oracle选择满足START WITH 条件的根记录 Oracle选择每条根记录的子行,每条子行满足CONNECT BY条件 Oracle选择上一步子行的逐代子行。即Oracle首先选择上一步子行的子行,然后在选取这些子行的子行,依次向下。Oracle总是计算当前父行的CONNECT BY条件来选择子行。什么意思呢?
Oracle使用了Prior操作符,PRIOR是一元操作符,作用于紧跟在它后面的字段名,如PRIOR EMPLOYEE_ID = MANAGER_ID,把该条件用于当前父行,PRIOR操作符导致Oracle取父行的EMPLOYEE_ID列的值,然后取子行的MANAGER_ID列的值与之比较,从而选出当前父行的子行。 如果查询包含一个无连接的WHERE子句,Oracle从层级中除去不满足WHE...
Oracle returns the rows in the order shown in Figure 9-1. In the diagram, children appear below their parents. For an explanation of hierarchical trees, see Figure 3-1. Figure 9-1 Hierarchical QueriesDescription of "Figure 9-1 Hierarchical Queries" To find the children of a parent row,...
LEVEL is a pseudocolumn for use in hierarchical queries. The LEVEL pseudocolumn returns the recursive step in the hierarchy at which a row was produced. All rows that are produced by the START WITH clause return the value 1. Rows that are produced by applying the first iteration of the CON...
Hierarchical queries 分层查询 A relational database does not store data in a hierarchical way. Then how do I get the data in a hierarchical manner? Here we get to know about how to use the hierarchical querying feature which Oracle has given. This article talks about how you can interpret ...
Hierarchical Queries A hierarchy is built upon a parent-child relationship within the same table or view.Hierarchical queryis one of the very first features of the Oracle Database. In a traditional query, Oracle looks for a good execution plan and retrieves the rows one after the other, in ...
The Anatomy of Functions of Hierarchical Queries Based on OracleOracle层次查询功能的剖析Oracle层次查询功能数据库树形结构软件项目中存在着大量的组织结构业务,Oracle数据库中的层次查询功能给程序员带来了极大方便,本文对其使用方法和灵活性进行了深入探讨.
CONNECT_BY_ROOT is a unary operator that is valid only in hierarchical queries. When you qualify a column with this operator, Oracle returns the column value using data from the root row. See the following query: SELECT emp_no,ename,job,manager_no,level,SYS_CONNECT_BY_PATH (ename,';')...
Please let me know whats the alternative for hierarchical queries of oracle . To be more precise - whats the replacement for "START WITH ... CONNECT BY PRIOR" clause of oracle in MySQL. best regards -Rajarshi Subject Views Written By Posted...