The Possibility of Writing an Infinite SQL Query

Can we write an SQL query that runs infinitely? The answer is yes, but with certain specific conditions. This article explores how to create such queries and the implications of doing so.

Creating Infinite Queries

While creating an infinite SQL query might seem counterintuitive, it is entirely possible, especially when using certain constructs. Here are a few ways to achieve this:

1. Recursive Common Table Expressions (CTEs)

A recursive CTE can be used to create an infinite loop if the termination condition is never met. Consider the following example:

WITH RECURSIVE infinite_cte AS 
(SELECT 1 AS num) 
UNION ALL 
SELECT num - 1 FROM infinite_cte
SELECT * FROM infinite_cte

This query will generate numbers indefinitely because there is no condition to stop the recursion.

2. Self-Join with No Termination Condition

An infinite result set can also be achieved with a self-join if there is no termination condition:

SELECT a.*
FROM your_table AS a
JOIN your_table AS b ON   

If your_table has no limits on the number of rows, this could lead to an infinite loop in terms of generating results.

3. Unbounded Loops in Procedural SQL

In languages like PL/pgSQL (PostgreSQL) or PL/SQL (Oracle), you can write a loop that never exits:

LOOP
   -- Some operation
END LOOP;

Although not directly visible in standard SQL, procedural SQL can be used to create such loops.

Considerations

Performance Impact: Infinite queries can have a severe impact on database performance, potentially leading to crashes or timeouts.

Practicality: While technically possible, such queries are typically impractical and should be avoided in production environments.

Conclusion

Although it is technically feasible to create infinite SQL queries, it is crucial to handle such scenarios carefully to avoid negative implications on system performance and stability.

For more information, see:

Cartesian Product - Wikipedia Join (SQL) - Wikipedia Hierarchical and Recursive Queries in SQL - Wikipedia

For specific examples, especially in Oracle, you might refer to the article Infinite loop in SQL.