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NTILE(): Splitting Rows Into Buckets

Use NTILE(4) to assign employees into salary quartiles.

Overview

NTILE(n) divides the ordered rows of a window into n roughly equal buckets, assigning each row a bucket number from 1 to n. It's the SQL way to compute percentiles/quartiles/tertiles for leaderboards and segmentation.

The Query

Employees & Departments

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Step-by-Step Breakdown

NTILE(4) — splits employees into 4 buckets (quartiles) by salary.
OVER (ORDER BY salary DESC) — bucket 1 holds the highest-paid quarter.
If rows don't divide evenly, the earlier buckets get the extra rows.

NTILE vs manual thresholds

NTILE is order-based, not value-based — bucket edges depend on row counts, not fixed salary cutoffs. Use it for ranking segments, not precise ranges.

Variations

Split movies into 3 budgets tiers (tertiles):

Movies (Movies/Actors/Ratings)

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Common Mistakes

Assuming equal value ranges. Buckets are sized by row count, so the salary gap between bucket 1 and 2 may differ from 2 to 3.
Non-deterministic ties. Rows with equal ORDER BY values may land in different buckets arbitrarily.
Forgetting ORDER BY. NTILE without an order has undefined bucket assignment.