While an index speeds up SELECT queries and WHERE clauses, it slows down data input in UPDATE and INSERT statements. There is no influence on the data when indexes are created or dropped.
Indexes are used by the query optimizer to speed up query execution. When preparing a SELECT, INSERT SELECT, UPDATE, or DELETE query, the optimizer leverages existing indexes or builds temporary indexes to generate an execution plan. A table's index is a map of keys to row locations.
By creating pointers to where data is stored within a database, indexing makes it easier to query columns. Assume you need to locate a specific piece of data in a vast database. To retrieve this data from the database, the computer will search every row until it finds it.
When referring to mathematical, scientific, or statistical situations, the term "indices" is used. It refers to the numbers, symbols, and figures that are used to compare a value to a standard. The term "indexes" is typically applied to written publications such as bibliographical or citation indexes.