Are Databases and Functional Programming at odds?

sql

data-integrity

functional-programming

database-performance

byAlex Kataev·Jan 29, 2025

In actuality, databases and functional programming can effectively complement each other, as they share commonalities in declarative patterns and immutability. SQL, being a declarative language, parallels functional programming's approach of stating what should be accomplished without specifying how to do it. Functional programming tenets such as recursive operations find equivalents in SQL's recursive common table expressions (CTEs) and deterministic functions.

Consider this SQL snippet, illustrating a recursive CTE, mirroring the logic often seen in a functional programming recursion:

-- Recursive CTE: it runs in circles, just like your dog when you say "fetch,"
-- but gets the job done, unlike your cat.
WITH RecursiveCTE AS (
    SELECT ID FROM Categories WHERE ParentID IS NULL -- start with the top dogs
    UNION ALL
    SELECT c.ID FROM Categories c JOIN RecursiveCTE r ON c.ParentID = r.ID -- get the underdogs
)
SELECT * FROM RecursiveCTE; -- fetch! Good boy, SQL server.

This query underlines the recursion in SQL imitating similar functionality in functional languages iterating over data structures.

Implementing Functional Patterns inside Relational Database Structures

Relational databases are based on set-theory, which shares fundamental aspects with functional programming. Thinking in terms of sets and set operations gives an edge while interacting with databases.

Building the Fort with Data Integrity

Database systems should take the lead in maintaining data integrity. SQL has been purpose-built not only to provide robust data integrity but also to efficiently manage system performance. In line with functional programming, SQL encourages immutable data structures.

Respecting Task Specialty and Paradigms

Use specialized tools engineered for database operations rather than attempting to shoehorn interfaces meant for other purposes. Remember the tasks handled by the database and those dealt in the user interface have different conceptual footprint.

Fitting the Paradigm to the Task

Functional programming libraries provide means to functionally harness databases effectively. Important advice here is adapt the paradigm to the task. This can mean using SQL for data manipulation tasks and a functional language like LISP for orchestrating business logic tasks.

Crafting Functional Interfaces and Dealing with State

Functional interfaces for databases need to wrestle with the challenge of state management, maintaining the stateless concept inherent in functional programming.

Balancing Efficiency and Pragmatic Constraints

It's crucial to balance the efficiency advantages with real-world constraints. The goal shouldn't be to shoehorn functional programming everywhere, but to carve out areas where it offers clear benefits without disrupting the inherent nature of databases.

Harmonizing Different Paradigms

Coalescing Paradigms for Holistic Solutions

Do not confine your solutions into a single paradigm. You can use functional programming, like data flow and stateless computations in concert with SQL's aptitude in data integrity and performance management.

Utilizing Functional Programming in Web Development

In web development, functional languages can interact with databases in a stateless way, much like how web browsers interact with servers.

Harness Functional Libraries for SQL interactions

Many functional libraries and tools exist that allow functional code to interact with SQL databases. These tools provide functions and abstractions that simplify the operation of databases.

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