What is Mutating table error?

The "Mutating table error" usually occurs in Oracle DBMS when attempting to modify (insert, update, or delete) data in a table that is already being used in the current query, such as in a trigger or subquery. This is due to a restriction that you cannot read and modify the same table simultaneously within a single statement to avoid unpredictable behavior.

For example: if in a trigger that fires on changes to table A, you try to update the same table A, this error will occur.

To work around this error, common approaches include:

• Using temporary tables for intermediate data
• Deferred execution of changes (e.g., via the DBMS_JOB package)
• Rewriting logic to avoid modifying the table within a trigger that is already in use.