Discussion
Which of the following is TRUE about mutating tables in PL/SQL triggers ?
Answer: A
Mutating tables cannot be queried or modified during trigger execution.
A table is 'mutating' while a DML statement is changing it. Oracle does not allow a row-level trigger on that table to read or change it, because the result would depend on the order in which rows happen to be processed. A trigger that tries raises the run-time error ORA-04091 (table is mutating, trigger/function may not see it).
So the table cannot be modified freely inside a row-level trigger. The problem shows at run time, not as a compilation error, and the restriction lasts only while the statement executes; nothing is locked permanently.
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