SQL PERCENT_RANK Function

Understanding PERCENT_RANK

The PERCENT_RANK window function calculates the relative rank of a row within a group of values. It returns a value between 0 and 1, representing the percentage of values that come before the current row. This makes it perfect for calculating percentiles and understanding relative positions within a dataset.

Basic Syntax

Common PERCENT_RANK Interview Questions

How would you find videos in the top 5% by views?
What's the difference between PERCENT_RANK and NTILE?
How can you calculate the relative position of each user's video performance?
How does PERCENT_RANK handle ties?

Common Usage Patterns

1. Basic Percentile Calculation

Calculate relative positions within the entire dataset.

2. Partitioned Percentile Analysis

Calculate relative rankings within groups.

3. Top Performer Analysis

Identify top performing content.

4. Multi-Metric Performance Analysis

Analyze relative performance across multiple metrics.

Best Practices for PERCENT_RANK

1. Understanding the Output

Know how PERCENT_RANK calculates values:

First row always gets 0
Last row always gets 1
Values represent relative position in dataset
Formula: (rank - 1) / (total_rows - 1)

2. Handling Ties

Manage tied values appropriately:

Tied values get same percentile rank
Consider additional columns for tie-breaking
Use DENSE_RANK for different tie behavior

3. Performance Optimization

Optimize your PERCENT_RANK queries:

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

Interview Master

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