Advanced SQL Techniques: Window Functions, Common Table Expressions, and More

by Alexander Griffin
Advanced SQL Techniques: Window Functions, Common Table Expressions, and More

Structured Query Language is foundational in the field of data analysis and management. SQL has grown from its modest origins as a query language for managing relational databases and developed into a robust toolset capable of complex analytics and intricate data manipulations. If you’re new to SQL or want to brush up on your abilities with a SQL Course, learning advanced techniques like subqueries, common table expressions (CTEs), and window functions will make a difference in your career. This blog will discuss these advanced SQL techniques, explaining what they are and how they work practically. Let’s start by understanding What is SQL.

Table Of Contents

  • Understanding SQL
  • Window Functions 
  • Common Table Expressions (CTEs)
  • Other Advanced SQL Techniques
  • Conclusion

Understanding SQL

A domain-specific language for managing and manipulating data stored in relational database management systems (RDBMS), Structured Query Language (SQL) is essential to understand. It offers a consistent syntax for many database-related tasks, including querying, updating, and structure definition. Data professionals in various industries rely on SQL because it is a universal language for connecting to databases.

Window Functions

One potent way to execute computations across a “window” of rows in a dataset is with window functions, also called analytics functions. Window functions keep the granularity of individual rows while computing aggregated values, in contrast to traditional aggregate functions that collapse multiple rows into a single result. 

Calculating cumulative totals, moving averages, and ranking results within partitions are common use cases for window functions. You can utilise window functions to rank customers according to their purchase frequency or to determine the total amount of sales for each product category over time. 

Common Table Expressions (CTEs)

An easy way to define temporary result sets within a SQL query is with Common Table Expressions (CTEs). CTEs simplify complex problems into smaller, more manageable pieces by optimising query readability and maintainability. 

The main query and the “WITH” clause are necessary components of a CTE. In the former, the CTE is defined. Using this modular approach to query construction, you can make your SQL code more organised and easy to maintain. It allows you to tackle complex data transformations step by step. 

Other Advanced SQL Techniques


SQL queries inside another query are called subqueries. Several sections of an SQL statement can be used to aggregate, filter, or correlate data from various tables. 

Subqueries often filter data using conditions that include calculations or aggregations from another table. Using a subquery, you can find out which products sell the best in each category or which customers have bought more than average.

Recursive Queries

Users can work with hierarchical data structures like organisational charts, bill-of-materials, or network graphs through recursive queries, also called hierarchical or recursive common table expressions (CTEs). Recursive queries can iteratively traverse hierarchical relationships within a table when a condition is satisfied. 

Take a hierarchical organization’s table, for example; it would have columns for manager ID, name, and employee ID. Regardless of the depth of the hierarchy, a recursive query can retrieve all employees reporting to a given manager and their subordinates. 

Pivot and Unpivot Operations

You can use the pivot and unpivot operations if you want to move data from one column to another or row to another. Data reformatting for reporting or dataset shaping for analysis are two applications of these operations that shine. 

For argument’s sake, assume you have a sales data table that includes columns for product categories and monthly sales amounts. A pivot operation can transpose the data to facilitate sales performance comparisons over time, allowing you to see monthly sales amounts for each product category. 

Analytical Functions

Analytical functions, sometimes called windowing functions or ranking functions, let users do calculations on a subset of rows in a result set. The analytical functions include a wider variety of operations, such as ranking, statistical calculations, lead/lag analysis, and window functions. 

Utilising analytical functions, one can sort products according to sales revenue, determine averages or standard deviations, find dataset outliers, or compare current values to those from the past or future.


It is possible to significantly improve one’s data manipulation and analysis skills by becoming proficient in advanced SQL techniques like subqueries, common table expressions (CTEs), and window functions. These methods give you vital tools to get insights out of your databases, whether you’re doing complicated calculations, aggregations, or data transformations. By mastering these advanced SQL techniques, data professionals can tackle complex data manipulation and analysis tasks, from working with hierarchical data structures to transforming and reshaping datasets for reporting and analysis.

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