Analysis of commonly used index classifications and advantages and disadvantages in Oracle

Commonly used index classification and analysis of advantages and disadvantages in Oracle

In Oracle database, index is an important database object, used to improve the efficiency of database retrieval data . Indexes can be divided into various categories based on the way and characteristics of indexing, and each index has its advantages and disadvantages. This article will introduce the commonly used index classifications in Oracle, analyze their advantages and disadvantages, and provide corresponding code examples.

1. Single column index

1. B-Tree index

B-Tree index is the most common index type and is suitable for equal value search and range search. It organizes data in the form of a binary tree, which can speed up retrieval. However, when the amount of data is large, B-Tree index may increase the index depth and affect query efficiency.

CREATE INDEX idx_name ON table_name(column_name);

2. Unique index

The unique index is similar to the B-Tree index, except that the unique index guarantees the numerical uniqueness of the index column. The unique index can effectively avoid the insertion of duplicate data and improve data integrity, but it requires additional checking constraints when inserting data, which has a certain impact on performance.

CREATE UNIQUE INDEX idx_name ON table_name(column_name);

3. Clustered index

Clustered index is an index type that aligns the physical order of the table with the logical order of the index. It sorts the data rows according to the value of the index column. Sort. Clustered indexes can reduce the number of IOs and increase query speed, but may affect performance during frequent insertion and deletion operations.

CREATE CLUSTER index_name ON table_name;

2. Multi-column index

1. Combined index

Combined index is an index composed of multiple columns, suitable for joint queries or multiple columns Conditional query. Combining indexes can reduce the number of indexes and save storage space, but attention should be paid to the impact of the order of index columns on query efficiency.

CREATE INDEX idx_name ON table_name(column1, column2);

2. Covering index

Covering index means that the index contains all columns required for query, which can avoid accessing the data table and improve query efficiency. However, attention should be paid to the selection of index columns to avoid excessively large indexes affecting performance.

CREATE INDEX idx_name ON table_name(column1) INCLUDE (column2, column3);

3. Special index

1. Full-text index

Full-text index is an index type specially used to retrieve text data and is suitable for full-text search and fuzzy queries. Full-text indexing can improve the efficiency of text data retrieval, but requires more resources in maintaining the index and occupying storage space.

CREATE FULLTEXT INDEX idx_name ON table_name(column_name);

2. Fuzzy query index

Fuzzy query index is a special index type used to support fuzzy query operations, such as the LIKE operator. Fuzzy query indexes can speed up fuzzy queries, but you need to pay attention to how wildcards are used.

CREATE INDEX idx_name ON table_name(column_name) NOPARALLEL;

To sum up, the commonly used index types in Oracle cover single-column indexes, multi-column indexes and special indexes. Each index type has its applicable scenarios, advantages and disadvantages. In practical applications, selecting the appropriate index type and rationally designing the index structure according to specific business needs and query scenarios can effectively improve the query performance of the database.

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