SQL Window Functions Cheat Sheet

Galaxy Glossary

What are window functions in SQL, and how do they differ from regular functions?

Window functions in SQL perform calculations over a set of rows related to the current row, without grouping the data. They're powerful for tasks like calculating running totals, ranking, and partitioning data.

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Description

Window functions are a powerful tool in SQL that allow you to perform calculations over a set of rows related to the current row, without grouping the data. Unlike aggregate functions (like SUM, AVG, COUNT), which summarize data across groups, window functions operate on a window of rows, providing insights into the context of each row. They're incredibly useful for tasks like calculating running totals, ranking records, and partitioning data for analysis. For instance, you might want to see how a sales figure for a particular day compares to the same day in the previous week or month. Window functions provide the framework for this type of analysis. A key distinction is that window functions don't change the shape of the result set; they add calculated columns to the existing rows. This makes them ideal for tasks that require context-sensitive calculations without losing the individual row details.

Why SQL Window Functions Cheat Sheet is important

Window functions are crucial for analytical tasks in SQL. They enable complex calculations on sets of related rows without losing individual row data, making them essential for reporting, data analysis, and business intelligence.

Example Usage


-- Create a table for customers
CREATE TABLE Customers (
    CustomerID INT PRIMARY KEY,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    City VARCHAR(50),
    Country VARCHAR(50)
);

-- Create a table for Orders
CREATE TABLE Orders (
    OrderID INT PRIMARY KEY,
    CustomerID INT,
    OrderDate DATE,
    TotalAmount DECIMAL(10, 2),
    FOREIGN KEY (CustomerID) REFERENCES Customers(CustomerID)
);

-- Insert some sample data
INSERT INTO Customers (CustomerID, FirstName, LastName, City, Country) VALUES
(1, 'John', 'Doe', 'New York', 'USA'),
(2, 'Jane', 'Smith', 'London', 'UK');

INSERT INTO Orders (OrderID, CustomerID, OrderDate, TotalAmount) VALUES
(101, 1, '2023-10-26', 100.50),
(102, 2, '2023-10-27', 150.00);

-- Create a view that shows customer names and total order amounts
CREATE VIEW CustomerOrders AS
SELECT
    c.FirstName || ' ' || c.LastName AS CustomerName,
    SUM(o.TotalAmount) AS TotalOrderAmount
FROM
    Customers c
JOIN
    Orders o ON c.CustomerID = o.CustomerID
GROUP BY
    CustomerName;

-- Query the view
SELECT * FROM CustomerOrders;

Common Mistakes

Forgetting to specify the `PARTITION BY` clause when working with multiple groups.
Using aggregate functions instead of window functions for calculations that need to retain individual row values.
Incorrectly ordering rows within the window using the `ORDER BY` clause.

SQL Window Functions Cheat Sheet

What are window functions in SQL, and how do they differ from regular functions?

Description

Why SQL Window Functions Cheat Sheet is important

Example Usage

Common Mistakes

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