Question - What Is An Index?
Answer -
You can create an index (also known as secondary key) to speed up the search for database records in a table. An index is a database object that can be defined for a single column or a sequence of columns of a database table.
In technical terms, indexes are data structures (consisting of one or more inverting lists), which store parts of the data of a table in a separate B* tree structure. This storage sorts the data according to the inverting key fields that were used. Due to this type of storage, the table data can be accessed faster using the indexed columns than without the relevant index.
Indexes, unlike tables, do not include any independent business data, and therefore can always be created again by the table. For example, this is relevant if corruption occurs on the index due to hardware problems.