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The `CREATE INDEX` statement is an SQL command used in a Database Management System (DBMS) to create an index on one or more columns of a table. An index is a special database object that helps the DBMS locate and retrieve records more quickly without scanning the entire table. It works in a similar way to the index of a book, where a reader can directly locate a particular topic instead of reading every page. In a database, indexes improve the speed of searching, sorting, joining, and filtering data. The basic syntax of the `CREATE INDEX` statement is: ```sql CREATE INDEX index_name ON table_name (column_name); ``` Here, `index_name` is the name given to the index, `table_name` specifies the table on which the index is created, and `column_name` represents the column whose values are indexed. For example, suppose there is a table named `STUDENT` containing the columns `STUDENT_ID`, `NAME`, `EMAIL`, and `COURSE`. An index on the `EMAIL` column can be created as: ```sql CREATE INDEX idx_student_email ON STUDENT (EMAIL); ``` After creating this index, the DBMS can find students based on their email addresses more efficiently, particularly when the table contains a large number of records. Indexes are mainly used to improve query performance. Consider the following query: ```sql SELECT * FROM STUDENT WHERE EMAIL = 'student@example.com'; ``` Without an appropriate index, the DBMS may have to examine many or all records in the `STUDENT` table to find the required email address. This is known as a table scan. If an index exists on the `EMAIL` column, the DBMS can use the index to locate the required record much faster. Therefore, indexes are particularly valuable when tables contain thousands, millions, or more records. An index can also be created on multiple columns. Such an index is called a composite or multi-column index. Its syntax is: ```sql CREATE INDEX idx_student_course_name ON STUDENT (COURSE, NAME); ``` This index contains values from both `COURSE` and `NAME`. It can be useful _____ _______ ___ __________ _______ _________ ______ ________ ____ ________ _____.
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