tailieunhanh - Managing Indexes

Classification of Indexes An index is a tree structure that allows direct access to a row in a table. Indexes can be classified based on their logical design or on their physical implementation. The logical classification groups indexes from an application perspective, while the physical classification is derived from the way the indexes are stored. Single column and concatenated indexes A single column index has only one column in the index key—for example, an index on the employees number column of an employees table. A concatenated index, also known as a composite index, is created on multiple columns in a table. Columns in a. | Managing Indexes Objectives After completing this lesson, you should be able to do the following: List the different types of indexes and their uses Create various types of indexes Reorganize indexes Maintain indexes Monitor the usage of an index Obtain index information Classification of Indexes Logical: Single column or concatenated Unique or nonunique Function-based Domain Physical: Partitioned or nonpartitioned B-tree: Normal or reverse key Bitmap Classification of Indexes An index is a tree structure that allows direct access to a row in a table. Indexes can be classified based on their logical design or on their physical implementation. The logical classification groups indexes from an application perspective, while the physical classification is derived from the way the indexes are stored. Single column and concatenated indexes A single column index has only one column in the index key—for example, an index on the employees number column of an employees table. A concatenated index, also known as a composite index, is created on multiple columns in a table. Columns in a concatenated index do not need to be in the same order as the columns in the table, nor do they need to be adjacent—for example, an index on the department and job columns of an employee table. The maximum number of columns in a composite key index is 32. However, the combined size of all the columns cannot exceed roughly one-half (minus some overhead) of the available data space in a data block. Classification of Indexes (continued) Unique and nonunique indexes Indexes can be unique or nonunique. Unique indexes guarantee that no two rows of a table have duplicate values in the key column (or columns). Nonunique indexes do not impose this restriction on the column values. Function-based indexes A function-based index is created when using functions or expressions that involve one or more columns in the table that is being indexed. A function-based index precomputes the value of the function or | Managing Indexes Objectives After completing this lesson, you should be able to do the following: List the different types of indexes and their uses Create various types of indexes Reorganize indexes Maintain indexes Monitor the usage of an index Obtain index information Classification of Indexes Logical: Single column or concatenated Unique or nonunique Function-based Domain Physical: Partitioned or nonpartitioned B-tree: Normal or reverse key Bitmap Classification of Indexes An index is a tree structure that allows direct access to a row in a table. Indexes can be classified based on their logical design or on their physical implementation. The logical classification groups indexes from an application perspective, while the physical classification is derived from the way the indexes are stored. Single column and concatenated indexes A single column index has only one column in the index key—for example, an index on the employees number column of an employees table. A concatenated .