Understanding Indexes in SQL

Can someone explain why indexes improve query performance? I get confused between clustered and non‑clustered indexes.

Sure! An index works like a book's table of contents. It lets the DB engine locate rows without scanning the whole table. A clustered index determines the physical order of data, while a non‑clustered index is a separate structure that points to the data rows.

Just a heads‑up: adding too many indexes can slow down INSERT/UPDATE operations because each write must also maintain the indexes.

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