tailieunhanh - Hierarchical Retrieval

After completing this lesson, you should be able to do the following: Interpret the concept of a hierarchical query Create a tree-structured report Format hierarchical data Exclude branches from the tree structure | Hierarchical Retrieval Schedule: Timing Topic 30 minutes Lecture 20 minutes Practice 50 minutes Total Objectives After completing this lesson, you should be able to do the following: Interpret the concept of a hierarchical query Create a tree-structured report Format hierarchical data Exclude branches from the tree structure Lesson Aim In this lesson, you learn how to use hierarchical queries to create tree-structured reports. Sample Data from the EMPLOYEES Table Sample Data from the EMPLOYEES Table Using hierarchical queries, you can retrieve data based on a natural hierarchical relationship between rows in a table. A relational database does not store records in a hierarchical way. However, where a hierarchical relationship exists between the rows of a single table, a process called tree walking enables the hierarchy to be constructed. A hierarchical query is a method of reporting, in order, the branches of a tree. Imagine a family tree with the eldest members of the family found . | Hierarchical Retrieval Schedule: Timing Topic 30 minutes Lecture 20 minutes Practice 50 minutes Total Objectives After completing this lesson, you should be able to do the following: Interpret the concept of a hierarchical query Create a tree-structured report Format hierarchical data Exclude branches from the tree structure Lesson Aim In this lesson, you learn how to use hierarchical queries to create tree-structured reports. Sample Data from the EMPLOYEES Table Sample Data from the EMPLOYEES Table Using hierarchical queries, you can retrieve data based on a natural hierarchical relationship between rows in a table. A relational database does not store records in a hierarchical way. However, where a hierarchical relationship exists between the rows of a single table, a process called tree walking enables the hierarchy to be constructed. A hierarchical query is a method of reporting, in order, the branches of a tree. Imagine a family tree with the eldest members of the family found close to the base or trunk of the tree and the youngest members representing branches of the tree. Branches can have their own branches, and so on. A hierarchical query is possible when a relationship exists between rows in a table. For example, in the slide, you see that employees with the job IDs of AD_VP, ST_MAN, SA_MAN, and MK_MAN report directly to the president of the company. We know this because the MANAGER_ID column of these records contain the employee ID 100, which belongs to the president (AD_PRES). Note: Hierarchical trees are used in various fields such as human genealogy (family trees), livestock (breeding purposes), corporate management (management hierarchies), manufacturing (product assembly), evolutionary research (species development), and scientific research. Natural Tree Structure De Hann King Hunold EMPLOYEE_ID = 100 (Parent) MANAGER_ID = 100 (Child) Whalen Kochhar Higgins Mourgos Zlotkey Rajs Davies Matos Gietz Ernst Lorentz Hartstein Fay Abel Taylor Grant Vargas