Indexing in a database improves query performance by allowing faster data retrieval. Instead of scanning the entire table, the database uses an index to locate rows efficiently. For example, in a users table with millions of records, searching for a user by email without an index would require checking every row (FULL TABLE SCAN). However, if an index is created on the email column (CREATE INDEX idx_email ON users(email);), the database can quickly locate the required record, significantly reducing query time. While indexing speeds up SELECT queries, it can slightly slow down INSERT and UPDATE operations due to index maintenance.
Example Analogy: Think of an index in a book. Instead of flipping through every page, you use the index to jump directly to the relevant section.
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