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Description

This error indicates a problem with the definition or structure of a recursive query, most commonly a `WITH RECURSIVE` Common Table Expression (CTE). It signifies that the database cannot correctly interpret or execute the intended recursion due to a syntax error or a violation of recursive query rules.

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Error Message

invalid recursion

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Known Causes

3 known causes

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Missing or Flawed Termination

Recursive CTEs require a base case and a condition to terminate the recursion. An absent or incorrectly defined termination logic can lead to an `invalid recursion` error.

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Incorrect Recursive Member Reference

The recursive part of a CTE must correctly refer to the CTE's own name. Misspellings or ambiguous references prevent the database from understanding the recursive step.

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Incompatible Data Types in UNION ALL

When combining the base and recursive members of a CTE with `UNION ALL`, the corresponding columns must have compatible data types. Mismatched types can invalidate the recursion.

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Solutions

3 solutions available

1. Correct Recursive CTE Termination Condition medium

Ensure your recursive CTE has a proper termination condition to prevent infinite loops.

1

Identify the recursive part of your Common Table Expression (CTE). This is typically the second `SELECT` statement within the `WITH RECURSIVE` block.

2

Review the `WHERE` clause or the join conditions in the recursive part. This is where the recursion should eventually stop.

3

Add or modify a condition to ensure that the recursive step does not produce new rows indefinitely. For example, if you are recursing through a hierarchy, stop when you reach a parent that doesn't exist or a certain depth.

-- Example: Stopping recursion when 'parent_id' is NULL
WITH RECURSIVE hierarchy AS (
    SELECT id, name, parent_id FROM employees WHERE id = 1
    UNION ALL
    SELECT e.id, e.name, e.parent_id FROM employees e JOIN hierarchy h ON e.parent_id = h.id WHERE e.parent_id IS NOT NULL
)
SELECT * FROM hierarchy;

4

Alternatively, if you are recursing based on a value (e.g., a counter), ensure that value eventually reaches a stopping point.

-- Example: Stopping recursion when counter reaches 10
WITH RECURSIVE counter AS (
    SELECT 1 AS n
    UNION ALL
    SELECT n + 1 FROM counter WHERE n < 10
)
SELECT * FROM counter;

2. Check for Self-Referencing without Progress medium

Verify that the recursive step is actually making progress towards the termination condition.

1

Examine the `SELECT` statement in the recursive part of your CTE. Ensure that it is joining to the CTE itself in a way that should eventually lead to the termination condition.

2

If the recursive step is simply joining back to the same set of rows without changing any values that contribute to the termination condition, you will get this error.

-- Incorrect example: No progress towards termination
WITH RECURSIVE infinite_loop AS (
    SELECT 1 AS val
    UNION ALL
    SELECT val FROM infinite_loop -- 'val' never changes, no termination
)
SELECT * FROM infinite_loop;

3

Modify the recursive `SELECT` to introduce a change that will eventually satisfy the termination condition. This might involve incrementing a counter, moving to a different related record, or filtering out rows that have already been processed.

-- Corrected example: Incrementing value
WITH RECURSIVE progress AS (
    SELECT 1 AS val
    UNION ALL
    SELECT val + 1 FROM progress WHERE val < 5
)
SELECT * FROM progress;

3. Limit Recursion Depth (for debugging or safety) easy

Temporarily limit the recursion depth to diagnose or prevent runaway CTEs.

1

Add a condition to your recursive CTE that limits the number of recursive steps. This can help identify if the recursion is indeed infinite or just very deep.

-- Add a 'depth' column and limit it
WITH RECURSIVE limited_recursion AS (
    SELECT id, name, parent_id, 0 AS depth FROM employees WHERE id = 1
    UNION ALL
    SELECT e.id, e.name, e.parent_id, lr.depth + 1 FROM employees e JOIN limited_recursion lr ON e.parent_id = lr.id WHERE lr.depth < 100 -- Limit to 100 levels
)
SELECT * FROM limited_recursion;

2

Run the query with the depth limit. If the query completes, your original issue was likely a very deep recursion or an infinite one. If it still errors, the problem is in the logic of the recursion itself.

3

Once diagnosed, remove the depth limit if the recursion should naturally terminate, or adjust the limit if it's a known deep but finite structure.

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Related Errors

5 related errors

PostgreSQL Error 42P19: Invalid Recursion Definition