Provide examples of common SQL window functions and their use cases.

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Aryan Kumar · Answer

Certainly! Here are some common SQL window functions and their typical use cases:
ROW_NUMBER():
Use Case: Assign a unique row number to each row within a result set. This can be helpful when you want to identify rows or establish a row's position within a partition.
SELECT
    ProductID,
    ProductName,
    ROW_NUMBER() OVER (ORDER BY ProductName) AS RowNum
FROM
    Products;
RANK() and DENSE_RANK():
Use Case: Rank rows within a result set, such as ranking products by sales or employees by performance.
RANK() assigns the same rank to rows with equal values, while 
DENSE_RANK() assigns consecutive ranks without gaps.
SELECT
   EmployeeName,
   Salary,
   RANK() OVER (ORDER BY Salary DESC) AS SalaryRank,
   DENSE_RANK() OVER (ORDER BY Salary DESC) AS DenseSalaryRank
FROM
   EmployeeData;
SUM() and AVG():
Use Case: Calculate cumulative sums or rolling averages over a defined window. Useful for financial and time-series analysis.
SELECT
   OrderDate,
   Revenue,
   SUM(Revenue) OVER (ORDER BY OrderDate) AS CumulativeRevenue,
   AVG(Revenue) OVER (ORDER BY OrderDate ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING) AS RollingAvgRevenue
FROM
   SalesData;
LEAD() and LAG():
Use Case: Access the values of the next or previous rows within a partition. Helpful for comparing current values with future or past values.
SELECT
    OrderDate,
    Revenue,
    LAG(Revenue) OVER (ORDER BY OrderDate) AS PrevRevenue,
    LEAD(Revenue) OVER (ORDER BY OrderDate) AS NextRevenue
FROM
    SalesData;
FIRST_VALUE() and LAST_VALUE():
Use Case: Retrieve the first and last values within a window. Useful for finding the start and end points of a particular range.
SELECT
    ProductName,
    Sales,
    FIRST_VALUE(ProductName) OVER (PARTITION BY Category ORDER BY Sales DESC) AS BestSellingProduct,
    LAST_VALUE(ProductName) OVER (PARTITION BY Category ORDER BY Sales DESC) AS WorstSellingProduct
FROM
    ProductSales;
NTILE():
Use Case: Divide data into equal-sized buckets or percentiles. It's often used for data distribution analysis.
SELECT
    StudentName,
    ExamScore,
    NTILE(4) OVER (ORDER BY ExamScore) AS Quartile
FROM
    ExamResults;
These examples showcase how SQL window functions can be used to perform various analytical tasks, including ranking, aggregation, trend analysis, and data partitioning. Depending on your specific analysis requirements, you can choose the appropriate window function to gain insights from your data.

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Provide examples of common SQL window functions and their use cases.

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