Database: Window Functions

Window functions are a powerful feature in databases that allow you to perform calculations across a set of rows related to the current row. They are commonly used in SQL queries to perform tasks such as ranking, aggregation, and summarization.

Syntax

Window functions are typically used in conjunction with the OVER clause. Here is the general syntax:

```sql SELECT column1, column2, window_function(column3) OVER (PARTITION BY column4 ORDER BY column5) FROM table_name; ```

Example

Let's consider a table named employees with columns employee_id, department_id, and salary. We can use window functions to calculate the average salary per department:

```sql SELECT employee_id, department_id, salary, AVG(salary) OVER (PARTITION BY department_id) AS avg_salary_per_dept FROM employees; ```

This query will return the average salary for each employee's department alongside their individual salary.

Use Cases

Window functions are commonly used in scenarios where you need to compare each row with others in a group. Some common use cases include calculating running totals, finding top N rows per group, and ranking results based on specific criteria.

Importance in Interviews

Understanding window functions is essential for anyone preparing for database-related interviews, especially for roles that require advanced SQL knowledge. Recruiters often test candidates on their ability to use window functions to solve complex problems efficiently.

Conclusion

Window functions are a valuable tool in database management, allowing for efficient data analysis and manipulation. By mastering window functions, you can enhance your SQL skills and tackle a wide range of analytical tasks with ease.

Tags: Database, SQL, Window Functions, Data Analysis, SQL Interview Questions