Mastering Recursive Queries in PostgreSQL for Graph Traversal

-By Abhishek Aggarwal


In the realm of relational database management systems, PostgreSQL stands out with its flexible features. Among its arsenal, the ability to perform recursive queries significantly sets it apart. But what are recursive queries, and how do they help in data management?

In a nutshell, recursive queries are your key to navigating through data structures like trees or graphs efficiently. This blog post invites you to explore PostgreSQL's unique recursive query feature and its practical application in graph traversal.

Imagine traversing your data like a pro, breezing through intricate structures like it's a walk in the park. With PostgreSQL's recursive queries, that's not just a dream. Let's dive into the fascinating world of PostgreSQL and see how it can make your data journey smoother!

Breaking Down Recursive Queries

Ready to uncover the magic of recursive queries in PostgreSQL? They are like a mirror reflecting on themselves! Recursive queries take the outcome of one query, whip it into the shape of a new query, and then get that new query rolling. This chain keeps going until it bumps into the termination condition.

When it comes to graph traversal, you can think of recursive queries as a tour guide. Starting from any node you choose, they'll take you on a journey, introducing you to all the neighboring nodes.

An Illustrative Problem

Imagine having a database table depicting a tree structure, where each node has a unique identifier and a parent identifier. For instance, consider this sample table definition:



parent_id INTEGER REFERENCES tree(id)


In this table, each row signifies a node in the tree. The id column represents a unique identifier for the node, and the parent_id column is a foreign key referencing the parent node. Now, let's say we want to find all the descendants of a given node in the tree. This is where a recursive query comes in.

Navigating Recursive Query Syntax in PostgreSQL

Here's how the syntax for a recursive query in PostgreSQL looks:

WITH RECURSIVE recursive_query_name (output_columns) AS (

  -- Base query (non-recursive part)

  SELECT output_columns

  FROM base_table

  WHERE termination_condition




  -- Recursive query

  SELECT output_columns

  FROM recursive_query_name

  JOIN other_tables ON join_condition

  WHERE recursion_condition


SELECT final_output_columns

FROM recursive_query_name;

The WITH keyword initiates a Common Table Expression (CTE)—a named, temporary result set that can be referenced within the same query. Adding the RECURSIVE keyword indicates that the CTE can call upon itself in a cycle.

This recursive query bifurcates into two sections: the non-recursive part, responsible for generating the initial result set, and the recursive part, which repeatedly executes using results from its prior cycle. This process continues until it hits a predefined termination condition.

The UNION operator weaves together the results from both the non-recursive and recursive parts. If the ALL keyword is included, duplicate results will be preserved.

The recursion happens when the recursive part of the query cites the CTE itself. The stopping point, or termination condition, is defined in the WHERE clause. As soon as this condition is met, the cycle of recursion halts.

Practical Example: Finding Tree Descendants

Using the tree table example, let's find all descendants of a node, for instance, node 1.

WITH RECURSIVE descendants AS (

SELECT id, parent_id

FROM tree

WHERE id = 1


SELECT, tree.parent_id

FROM tree

JOIN descendants ON tree.parent_id =



FROM descendants;

Here's a quick breakdown of what happens:

The query result is a set of rows, each containing the id of a descendant of node 1.

Final Thoughts

Stepping into the fascinating world of PostgreSQL, did you know its recursive query feature is like a secret weapon when it comes to graph traversal? You see, by tying together the recursive query syntax and Common Table Expressions (CTEs), PostgreSQL lets you navigate through complex graph-like structures almost effortlessly. Think of it like having a super-powered GPS for your data!

This nifty feature lights up the path for intricate operations and in-depth data analysis. It's like exploring connections, unravelling mysteries, and making exciting discoveries. PostgreSQL is like a multi-tool in your data management toolbox, standing as a top-tier choice for applications playing around with graph data.

So, why not take a plunge into the PostgreSQL universe and unleash the potential of recursive queries? The journey promises to be a roller coaster, where you unlock infinite possibilities for graph traversal. Remember, in the world of PostgreSQL, every data challenge is just an opportunity in disguise!

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