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Learn Advanced SQL with Databricks

Learn Advanced SQL with Databricks

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Vipin
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3 min read

Introduction

In this blog post, we'll explore advanced SQL techniques that are essential for complex data analysis and manipulation. By mastering these SQL features, you can write more efficient queries and gain deeper insights from your data.

Table of Contents

  1. Common Table Expressions (CTE)

    • What is a CTE?

    • Benefits of using CTEs

    • Example of using CTEs

  2. Subqueries

    • What is a Subquery?

    • Types of Subqueries (Scalar, Row, and Table Subqueries)

    • Examples of Subqueries

  3. Window Functions

    • Introduction to Window Functions

    • Types of Window Functions (ROW_NUMBER, RANK, DENSE_RANK, etc.)

    • Example of using Window Functions

  4. SQL Ranking

    • Understanding SQL Ranking Functions

    • Examples of Ranking Functions (ROW_NUMBER, RANK, DENSE_RANK)

    • Use Cases and Examples

  5. UNION Operator

    • Introduction to UNION and UNION ALL

    • Differences between UNION and UNION ALL

    • Example of using UNION

Sample test data files for Hands-on

  1. Employee:https://github.com/vipinputhanveetil/ctb_blog_demo_files/blob/main/databricks_files/employees.csv

  2. Orders: https://github.com/vipinputhanveetil/ctb_blog_demo_files/blob/main/databricks_files/orders.csv

  3. Products: https://github.com/vipinputhanveetil/ctb_blog_demo_files/blob/main/databricks_files/products.csv

  4. Sales: https://github.com/vipinputhanveetil/ctb_blog_demo_files/blob/main/databricks_files/sales.csv

  5. Archived products: https://github.com/vipinputhanveetil/ctb_blog_demo_files/blob/main/databricks_files/archived_products.csv

Common Table Expressions (CTE)

What is a CTE?

A CTE (Common Table Expression) is a temporary result set that you can reference within a SELECT, INSERT, UPDATE, or DELETE statement.

Benefits of using CTEs

  • Improves readability of complex queries.

  • Enables recursive queries.

  • Avoids repetition of subqueries.

Example of using CTEs

-- Example: Find employees with salary above average
WITH avg_salary AS (
    SELECT AVG(salary) AS average_salary
    FROM employees
)
SELECT employee_id, first_name, last_name, salary
FROM employees
WHERE salary > (SELECT average_salary FROM avg_salary);

2. Subqueries

What is a Subquery?

A subquery is a query nested inside another query.

Types of Subqueries

  • Scalar Subquery: Returns a single value.

  • Row Subquery: Returns one or more rows.

  • Table Subquery: Returns an entire table.

Examples of Subqueries

--Example: Find orders with amounts greater than the average order amount
SELECT order_id, amount
FROM orders
WHERE amount > (SELECT AVG(amount) FROM orders);

3. Window Functions

Introduction to Window Functions

Window functions perform calculations across a set of table rows related to the current row.

Types of Window Functions

  • ROW_NUMBER

  • RANK

  • DENSE_RANK

  • LEAD and LAG

4. SQL Ranking

Understanding SQL Ranking Functions

SQL Ranking functions assign a rank to each row within a partition of a result set.

Examples of Ranking Functions

--Example: Rank employees by salary
SELECT employee_id, first_name, last_name, salary,
       RANK() OVER (ORDER BY salary DESC) AS salary_rank
FROM employees;

5. UNION Operator

Introduction to UNION and UNION ALL

The UNION operator is used to combine the result sets of two or more SELECT statements. It removes duplicates by default, while UNION ALL retains duplicates.

Example of using UNION

-- Example: Combine results from two queries
SELECT product_id, product, category
FROM products
UNION
SELECT product_id, product, category
FROM archived_products;

Conclusion

These advanced SQL techniques provide powerful tools for data analysis and manipulation. By incorporating CTEs, Subqueries, Window Functions, SQL Ranking, and UNION into your SQL toolbox, you can handle complex queries and gain deeper insights from your databases.

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