Oracle 索引使用语法指南（oracle索引语法）

Oracle Indexes Usage Syntax Guide

Indexes are data structures, which are used to speed up the retrieval of data from the Oracle database. Indexes enable data to be organized and quickly retrieved without having to search through all the data in the table. In Oracle, indexes can be created in both single attributes and in groups of attributes.

In Oracle, indexes are created with the CREATE INDEX statement. The syntax for the Oracle CREATE INDEX statement is as follows:

CREATE INDEX index_name

ON table_name

(column_name(s));

In this syntax, the index_name specifies the name of the index that is being created, and the table_name specifies the name of the table where the index will be created. The column_name specifies the name of the column that the index will be created on. Additionally, grammatical variations of the Oracle CREATE INDEX statement supported by Oracle include the following:

CREATE INDEX index_name

ON (column_name, column_name…)

TABLESPACE tablespace_name;

CREATE BITMAP INDEX index_name

ON table_name

(column_name(s));

CREATE UNIQUE INDEX index_name

ON table_name

(column_name(s));

In this syntax, the TABLESPACE clause can be used to specify the tablespace to store the index of the specified table. The BITMAP keyword can be used to create an index as a bitmap in the specified table. The UNIQUE keyword can be used to create a unique index in the specified table.

Once the index is created, it must be maintained. Oracle provides the ALTER INDEX statement to maintain indexes. The syntax of the ALTER INDEX statement is as follows:

ALTER INDEX index_name

{REBUILD | COALESCE}

[WITH {INDEX | INDEXES} (column_name(s))]

[TABLESPACE tablespace] ;

Here, the REBUILD keyword is used to rebuild the index and the COALESCE keyword is used to coalesce the index. The WITH INDEX clause is used to add columns to the index, and the WITH INDEXES clause is used to add multiple columns to the index. The TABLESPACE clause is used to specify the tablespace to store the index of the specified table.

Oracle also provides the DROP INDEX statement to delete an index from the database. The syntax of the DROP INDEX statement is as follows:

DROP INDEX index_name;

In this syntax, the index_name specifies the name of the index that is being dropped.

Once an index is created, it can be used to query the data in the Oracle table. The syntax of the query is as follows:

SELECT *

FROM table_name

WHERE column_name = expression

Here, the SELECT statement retrieves data from the Oracle table. The WHERE clause is used to specify the search criteria. The column_name is the index and the expression is the value that will be used to search in the indexed column.

In conclusion, indexes are data structures which are used to speed up the retrieval of data from the Oracle database. By using the CREATE INDEX statement, the ALTER INDEX statement, and the DROP INDEX statement, an Oracle index can be created, maintained, and deleted. Once an index is defined, an Oracle query can be used to search through the data in the indexed columns.