SQL NTILE Function

Understanding NTILE

The NTILE window function divides ordered rows into a specified number of approximately equal groups (buckets). It's particularly useful for creating percentiles, quartiles, or any custom number of groupings. Each row is assigned a bucket number based on its position in the ordered set.

Basic Syntax

Common NTILE Interview Questions

How would you divide videos into quartiles based on view count?
How can you identify the top 10% of performing videos for each user?
What happens when the number of rows isn't evenly divisible by the bucket count?
How would you create a 5-star rating system based on view counts?

Common Usage Patterns

1. Creating Quartiles

Divide data into four equal groups.

2. Percentile Analysis

Create fine-grained percentile buckets.

3. Custom Rating System

Create a rating system based on performance metrics.

4. Multi-Metric Bucketing

Create buckets based on multiple performance metrics.

Best Practices for NTILE

1. Understanding Bucket Distribution

Know how NTILE handles uneven distributions:

Larger buckets are assigned to the first groups
Difference between largest and smallest bucket is at most 1
Consider row count when choosing bucket number

2. Choosing Bucket Size

Select appropriate number of buckets:

Common choices: 4 (quartiles), 5 (quintiles), 10 (deciles), 100 (percentiles)
Consider data size and analysis goals
Too many buckets can lead to meaningless groupings

3. Performance Considerations

Optimize your NTILE queries:

Index columns used in ORDER BY and PARTITION BY
Filter data before applying NTILE
Consider materialized views for frequent calculations

Interview Master

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