System Design · Junior · Question 59 of 75

What does a database index do?

✓Correct answer: Speeds up searching by a column using an extra data structure, at the cost of slower writes and more storage
2Encrypts the table
3Counts rows automatically

Explanation

Without an index, filtering scans the whole table. Index columns used in WHERE, JOIN and ORDER BY of frequent queries.

Further reading

Wikipedia: Database index ↗

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