ORA-54012 is caused when you try to create a table where one virtual column is attempting to reference a different virtual column. Oracle has created the restriction of preventing one virtual column from referencing another. This helps to prevent complexities such as infinite loops. For example, column “A” might try to reference column “B” and column “B” might also reference column “A”.
If you’re needing computed values based on other computed values, consider creating a view with an expression that references the multiple virtual columns.
Note that views may be useful in other ways with virtual columns as well.
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