Oracle -PL-SQL-Trigger – Old and New Column Values
Within a trigger body of a row trigger, two correlation names exist for every column of the table being modified: one for the old column value, and one for the new column value. Depending on the type of triggering statement, certain correlation names might not have any meaning. A trigger fired by an INSERT statement has meaningful access to new column values only. Because the row is being created by the INSERT, the old values are null. A trigger fired
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