Databases · Junior · Question 73 of 75

Does PostgreSQL automatically create an index on a foreign key column like `orders.user_id`?

✓Correct answer: No; only primary keys and unique constraints get indexes automatically, so you usually add one yourself
2Only if the table has more than 1000 rows
3Yes, always

Explanation

Without an index, joins by user_id and deletes of users (which check for referencing orders) have to scan the whole orders table.

Further reading

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