1. Introduction to Window Functions

Window functions perform calculations across a set of table rows related to the current row. Unlike aggregate functions, they do not group the result into a single output row, allowing access to individual rows while performing aggregate-like calculations.

Syntax of Window Functions

function_name(expression) OVER (
    [PARTITION BY column_name]
    [ORDER BY column_name]
)

2. Common Use Cases of Window Functions

a. Ranking

• Functions: ROW_NUMBER(), RANK(), DENSE_RANK()
• Use Case: Identifying the top performers or assigning unique row IDs in a dataset.

b. Aggregates

• Functions: SUM(), AVG(), MIN(), MAX(), COUNT()
• Use Case: Calculating running totals, moving averages, or cumulative distributions.

c. Percentile and Distribution

• Functions: PERCENT_RANK(), NTILE(), CUME_DIST()
• Use Case: Allocating rows into percentiles or analyzing distribution patterns.

d. Lag/Lead

• Functions: LAG(), LEAD()
• Use Case: Comparing values of a column with its previous or next rows.

e. First/Last Value

• Functions: FIRST_VALUE(), LAST_VALUE()