How to Resolve MySQL Error: 'Can't update table 'x' in stored function/trigger because it is already used by a statement which invoked this stored function/trigger'?

MySQL Error: Trigger Update Conflict

When attempting to execute a MySQL query involving a trigger, users may encounter the error: "Can't update table 'x' in stored function/trigger because it is already used by a statement which invoked this stored function/trigger."

Understanding the Error

This error arises when the trigger attempts to modify the same table that it's associated with while the triggering event is occurring. In this case, the error occurs within an AFTER INSERT trigger on the brandnames table. The trigger is attempting to update the bname column with a capitalized version of the input value.

Why Does it Occur?

MySQL prevents updating a table from within a trigger for two reasons:

1. Potential Deadlocks: Updates within a trigger can lead to deadlocks if the triggering event involves table locking.
2. Infinite Loop: Updating the triggered table from within the trigger would cause the trigger to be triggered again, creating an infinite recursive loop.

Resolution

To resolve this error, avoid updating the triggered table within the trigger itself. Instead, consider the following alternatives:

• Using NEW and OLD: Access the newly inserted or updated values using the NEW and OLD pseudo-tables, as demonstrated in the provided answer.
• Modifying Data Before Triggering: If possible, modify the data before the trigger is invoked. For example, in the case of capitalizing brand names, this can be done before inserting the record.

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