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Description

This error indicates that a MySQL stored function or trigger is attempting to call itself, either directly or indirectly. MySQL strictly prohibits recursive calls in stored routines to prevent infinite loops, server crashes, and resource exhaustion. It typically arises when defining or executing database logic that creates a self-referencing cycle.

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Error Message

Recursive stored functions and triggers are not allowed.

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Known Causes

4 known causes

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Direct Self-Call

A stored function or trigger explicitly contains logic that calls itself within its own definition.

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Indirect Circular Call

Two or more stored routines (functions, procedures, or triggers) call each other in a loop, such as Function A calling Function B, which then calls Function A.

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Trigger Self-Modification

An `AFTER INSERT`, `AFTER UPDATE`, or `AFTER DELETE` trigger on a table attempts to modify the same table in a way that would cause the trigger to fire again for the same operation.

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Unintended Logic Flow

Complex or nested routine calls unintentionally lead back to the original routine, forming a recursive path due to intricate database logic.

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Solutions

3 solutions available

1. Refactor Recursive Logic into Iterative Approach advanced

Rewrite the stored function or trigger to use loops instead of recursion.

1

Analyze the existing recursive logic within your stored function or trigger. Identify the base case(s) and the recursive step(s).

2

Rewrite the logic using iterative constructs like `WHILE` loops or `LOOP` statements in SQL. You will likely need to manage state variables manually, similar to how the recursion stack would have handled it.

Example of converting recursion to iteration (conceptual):

-- Original Recursive Function (Conceptual)
-- DELIMITER $$
-- CREATE FUNCTION recursive_sum(n INT) RETURNS INT
-- BEGIN
--     IF n <= 0 THEN
--         RETURN 0;
--     ELSE
--         RETURN n + recursive_sum(n - 1);
--     END IF;
-- END$$

-- Iterative Function
DELIMITER $$
CREATE FUNCTION iterative_sum(n INT) RETURNS INT
BEGIN
    DECLARE sum_val INT DEFAULT 0;
    DECLARE counter INT DEFAULT n;
    WHILE counter > 0 DO
        SET sum_val = sum_val + counter;
        SET counter = counter - 1;
    END WHILE;
    RETURN sum_val;
END$$

3

Test the new iterative function or trigger thoroughly to ensure it produces the same results as the original recursive logic and handles all edge cases correctly.

2. Break Down Complex Logic into Multiple Functions/Triggers medium

Divide the recursive task into smaller, non-recursive components.

1

Identify the part of your stored function or trigger that is causing the recursion. This might be a call to itself or another function/trigger that eventually calls back to the original.

2

Create new, separate stored functions or triggers that handle specific sub-tasks. Ensure these new components do not call back to the original recursive entity or create a circular dependency.

Example: If a trigger on `orders` calls a function `process_order` which then calls another function `update_inventory` that somehow ends up calling `process_order` again. Instead, `process_order` could call `update_inventory` directly if `update_inventory` is designed to be non-recursive.

3

Modify the original stored function or trigger to call these new, independent components in a sequential or conditional manner, effectively flattening the call chain.

3. Re-evaluate Trigger Design and Event Firing medium

Ensure triggers are not unintentionally firing in a recursive loop by modifying their conditions or the order of operations.

1

Examine the `CREATE TRIGGER` statement and the statements within the trigger body. Identify if the trigger is performing an action that, in turn, causes the same trigger to fire again (e.g., an `UPDATE` statement on the same table the trigger is associated with).

Example: A trigger on `users` that `UPDATE`s the `users` table itself without a proper condition.

-- Incorrect Trigger Example
-- DELIMITER $$
-- CREATE TRIGGER user_update_trigger
-- AFTER UPDATE ON users
-- FOR EACH ROW
-- BEGIN
--     UPDATE users SET last_modified = NOW() WHERE user_id = NEW.user_id;
-- END$$

2

Implement specific conditions within the trigger to prevent re-execution. This can involve checking `OLD` and `NEW` values, or using session variables to track if the trigger has already executed for a given operation.

Corrected Trigger Example:

DELIMITER $$
CREATE TRIGGER user_update_trigger
AFTER UPDATE ON users
FOR EACH ROW
BEGIN
    -- Only update if last_modified is different to prevent infinite loops
    IF OLD.last_modified <> NEW.last_modified THEN
        UPDATE users SET last_modified = NOW() WHERE user_id = NEW.user_id;
    END IF;
END$$

3

Consider the order of operations if multiple triggers are involved. MySQL executes triggers in the order they are created (or alphabetically by name if not explicitly ordered). Reordering or renaming triggers might resolve circular dependencies.

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Related Errors

5 related errors

MySQL Error 1424: Recursive Call Not Allowed