What are Indexes in SQL Database? What is the advantage and disadvantage of Indexes?

What are Indexes in SQL Database? What is the advantage and disadvantage of Indexes?

Indexes are schema objects in a SQL database that can boost query performance while executing queries with a filter condition using where clause.

Indexes are used to retrieve data from databases very fast. An Index is a quick lookup table that is used to find a record that user search very frequently. An index helps to speed up select queries and where clauses, but it slows down data input, with the update and the insert statements.