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,child出现在他们parent的...
Oracle returns the rows in the order shown inFigure 9-1. In the diagram, children appear below their parents. For an explanation of hierarchical trees, seeFigure 3-1. Figure 9-1 Hierarchical Queries Description of "Figure 9-1 Hierarchical Queries" ...
SQL Server has not made it easy to represent and store them in relational tables. After SQL Server2000, XML structures are excellent for managing hierarchical data relationships, of course in SQL Server 2005, developers can use recursive queries against data stored hierarchically, but it needs...
You must specify LEVEL in the context of a hierarchical query. You cannot specify LEVEL in the START WITH clause, as an argument of the CONNECT_BY_ROOT operator, or as an argument of the SYS_CONNECT_BY_PATH function (SQLSTATE 428H4). Unary operators that support hierarchical queries are C...
In this guide, you’ll learn what hierarchical data is, see several different methods for designing your tables along with queries for each method, pros and cons of each design, and recommendations for Oracle, SQL Server, MySQL, and PostgreSQL. ...
In the next lesson, you will compare theINTERSECT,MINUS, andUNIONcommands. Hierarchical Retrieval - Exercise Click the Exercise link below to practice writing queries. Hierarchical Retrieval - Exercise [1]recursive SQL Query:A recursive SQL query in Oracle is a type of query that iteratively proces...
In Oracle, hierarchical queries are used to query data that has a parent-child relationship where each child can have only one parent, whereas a parent can have multiple children. This is very useful when trying to build reporting queries such as product lineage, manager reports, and a family...
Now the tables are propulated and you can run the appropriate queries, for example a query on PLSQL_PROFILER_RUNS. Copy code snippet Copied to Clipboard Error: Could not Copy Copied to Clipboard Error: Could not Copy SQL> select runid, run_date, run_comment from plsql_profiler_runs; ...
In most of these situations, consider what the query is trying to accomplish and rewrite it to use the emulation. References For more information, check out the following references. Migrating Oracle to SQL Server 2008 White Paper Recursive Queries Using Common T...
Hierarchical queries Suggest edits Ahierarchical queryis a type of query that returns the rows of the result set in a hierarchical order based on data forming a parent-child relationship. A hierarchy is typically represented by an inverted tree structure. The tree is made up of interc...