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What is mutation in the trigger?
The error is encountered when a row-level trigger accesses the same table on which it is based, while executing. The table is said to be mutating. Mutation will not occur if a single record is inserted in the table (using VALUES clause).
How do you avoid mutating table errors?
The Oracle mutating trigger error occurs when a trigger references the table that owns the trigger, resulting in the “ORA-04091: table name is mutating, trigger/function may not see it.” message. Don’t use triggers – The best way to avoid the mutating table error is not to use triggers.
What is a mutating table error and how can you get around it?
A mutating table error (ORA-04091) occurs when a row-level trigger tries to examine or change a table that is already undergoing change (via an INSERT, UPDATE, or DELETE statement). In particular, this error occurs when a row-level trigger attempts to read or write the table from which the trigger was fired.
Can a statement Level trigger be used on a mutating table?
If a trigger does result in a mutating table error, the only real option is to rewrite the trigger as a statement-level trigger. Mutating table errors only impact row level triggers. But to use a statement level trigger, some data may need to be preserved from each row, to be used by the statement level trigger.
What causes a mutating table / trigger error in Oracle?
A simple row level trigger that causes a mutating table error can result in a very complicated statement level trigger to achieve the needed result. Here are some important items to remember about triggers. On insert triggers have no :OLD values. On delete triggers have no :NEW values. Triggers do not commit transactions.
Is there a way to avoid the mutating table error?
Don’t use triggers – The best way to avoid the mutating table error is not to use triggers. While the object-oriented Oracle provides “methods” that are associated with tables, most savvy PL/SQL developers avoid triggers unless absolutely necessary.
Why does my trigger keep mutating every other session?
Every other session sees only the committed results. The mutating issue surfaces when a regular trigger attempts to modify the same table that was modified by the driving insert, update or delete statement.