Virtual Columns

#VirtualColumns
#Oracle
The syntax for defining a virtual column is listed below.
column_name [datatype] [generated always] as (expression) [virtual]
If the datatype is omitted, it is determined based on the result of the expression. The GENERATED ALWAYS and VIRTUAL keywords are options, and provided for clarity only.

Restrictions
Notes and restrictions on virtual columns include:

Indexes defined against virtual columns are equivalent to function-based indexes.
Virtual columns can be referenced in the WHERE clause of updates and deletes, but they cannot be manipulated by DML.
Tables containing virtual columns can still be eligible for result caching.
Functions in expressions must be deterministic at the time of table creation, but can subsequently be recompiled and made non-deterministic without invalidating the virtual column. In such cases the following steps must be taken after the function is recompiled:
Constraint on the virtual column must be disabled and re-enabled.
Indexes on the virtual column must be rebuilt.
Materialized views that access the virtual column must be fully refreshed.
The result cache must be flushed if cached queries have accessed the virtual column.
Table statistics must be regathered.
Virtual columns are not supported for index-organized, external, object, cluster, or temporary tables.
The expression used in the virtual column definition has the following restrictions:
It cannot refer to another virtual column by name.
It can only refer to columns defined in the same table.
If it refers to a deterministic user-defined function, it cannot be used as a partitioning key column.
The output of the expression must be a scalar value. It cannot return an Oracle supplied datatype, a user-defined type, or LOB or LONG RAW. #ORA
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