Exploring Common Table Expressions and Window Functions

Developers are often challenged to deliver results that are hard to implement using simple SQL queries.  Fortunately, complex SQL capabilities exist in the SQL standards --- common table expressions and window functions.

SQL is a declarative language, meaning the user submits an SQL command and the database determines the optimal execution. Common Table Expressions (CTEs) allow queries to be more imperative, allowing looping and processing hierarchical structures that are normally associated only with imperative languages.

Normal SQL queries return rows where each row is independent of the other returned rows. SQL window functions allow queries to return computed columns based on values in other rows in the result set.

This tutorial will help developers use CTE queries in their applications and allow operations that normally could only be done in application code to be done via SQL queries.  It also explains the many window function facilities and how they can be used to produce useful SQL query results.