Seq scan vs index scan

Learn table scan vs index scan.

Seq scan vs index

A Seq scan scans the whole table. An Index scan uses the index, which is faster.

-- Seq Scan: WHERE price > 0 (tüm tablo)
-- Index Scan: WHERE id = 5 (indeks)

Seq slow, index fast.

Seq scan is fine on small tables. On large tables, adding an index speeds things up.

For example, if you search a table with millions of orders by customer_id, an index on that column turns a Seq Scan into an Index Scan.

Use EXPLAIN to see if a query uses a seq scan or an index scan.

Show example solution

EXPLAIN SELECT * FROM products WHERE id = 5;

Index scan

____ → uses an index

Show answer

Index scan → uses an index

Next lesson: Cost