What is an index?
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An index is the same as alias.
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An index is a special way to join 2 or more tables.
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An index is a database table attribute, which speeds-up data search within a table.
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An index is a database row attribute, which speeds-up data search within a table.
An index is a database object associated with a table that creates a fast lookup path to rows, dramatically speeding up data retrieval operations. Indexes work like a book's index: instead of scanning every page, you jump directly to the relevant location. Option D is incorrect because indexes operate at the table level, not on individual rows.
An index is a database object built on one or more columns of a table that allows the database engine to locate rows much faster than scanning the whole table. It doesn't store the actual row data itself (unlike an alias, which is just an alternate name) — it's a separate lookup structure that speeds up searches and queries.