Ranking Functions

Ranking functions are a specialized category of SQL window functions designed to assign ranks or numbers to rows within a partition. Common ranking functions include ROW_NUMBER(), RANK(), DENSE_RANK(), and NTILE().

Overview of Ranking Functions

ROW_NUMBER()

• Functionality: Assigns a unique sequential integer to rows within a partition.
• Syntax:

ROW_NUMBER() OVER (PARTITION BY column_name ORDER BY column_name)

RANK()

• Functionality: Assigns a rank with gaps between ranks if there are ties.
• Syntax:

RANK() OVER (PARTITION BY column_name ORDER BY column_name)

DENSE_RANK()

• Functionality: Assigns consecutive ranks without gaps for ties.
• Syntax:

DENSE_RANK() OVER (PARTITION BY column_name ORDER BY column_name

NTILE()

• Functionality: Distributes rows into a specified number of approximately equal groups.
• Syntax:

NTILE(n) OVER (PARTITION BY column_name ORDER BY column_name)

Practical Examples

ROW_NUMBER() Example

SELECT employee_id, 
       salary, 
       ROW_NUMBER() OVER (PARTITION BY department_id ORDER BY salary DESC) AS row_num
FROM employees;

RANK() Example

SELECT employee_id, 
       salary, 
       RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) AS rank
FROM employees;

DENSE_RANK() Example

SELECT employee_id, 
       salary, 
       DENSE_RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) AS dense_rank
FROM employees;

NTILE() Example

SELECT employee_id, 
       salary, 
       NTILE(4) OVER (PARTITION BY department_id ORDER BY salary DESC) AS quartile
FROM employees;

Applications

• Performance Ranking:
  Rank employees or products based on metrics.
• Statistical Grouping:
  Distribute data into quartiles, deciles, etc.
• Leaderboard Generation:
  Create ranked lists for competitive analysis.

Benefits

• Simplified Ranking:
  Easily assign ranks or group numbers.
• Enhanced Data Insights:
  Provides clarity on relative standings within partitions.
• Flexible Analysis:
  Supports various ranking and grouping scenarios.