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📚 WINDOW FUNCTION

Window functions in SQL perform calculations across a set of table rows that are related to the current row.
Unlike aggregate functions, they do not collapse the result set.

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🛠️ Basic Syntax

SELECT column1, 
       window_function() OVER (PARTITION BY column2 ORDER BY column3)
FROM table_name;

• OVER defines the window of rows to apply the function to.
• PARTITION BY divides the result set into groups.
• ORDER BY specifies the order of rows within each partition.

Example

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

• This query ranks employees by salary within each department.

Key Points

• Common window functions: ROW_NUMBER(), RANK(), DENSE_RANK(), SUM(), AVG().
• PARTITION BY is optional — if omitted, the entire result set is treated as a single partition.
• ORDER BY inside the OVER clause controls the row order for the function.

Additional Example

SELECT order_id, customer_id, 
       ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY order_date) AS order_sequence
FROM orders;

• This query numbers each customer's orders starting from 1.

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🎥 Video Notes

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📝 Problem Description

Describe the problem, challenge, or topic discussed in a video related to SELECT FROM.
What concept was explained or what exercise was solved?

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DataBase Given

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💻 My SQL Code

-- Write your SQL code attempt or solution related to SQL COMMAND
SQL COMMAND

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🧠 Solution Code / Explanation

SQL COMMAND

Explanation - Explain what you learned, any key takeaways, or how you solved the problem related to COMMAND._

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