This clause instructs the database to sort the rows of the cluster on this column after applying the hash function when performing a DML operation. Rather, the database derives the values in a virtual column on demand by computing a set of expressions or functions.Doing so may improve response time during subsequent operations on the clustered data. Virtual columns can be used in queries, DML, and DDL statements.If the first element of the variable name already references a hash array then the variable update will affect the original variable.This behaviour can be a little unpredictable (and may well be improved upon in a future version).If you're not worried about preserving variable values, or you trust the templates you're including then you might prefer to use the directive.However, be aware that because of the localisation issues explained above (if you skipped the previous Technical Note above then you might want to go back and read it or skip this section too), the variables might not actually be "local".This might be what you want, of course, but then again, it might not.
You can specify at most one valid time dimension when you create a table.in evaluating the variable named, but doesn't print the result returned.This can be useful when a variable is bound to a sub-routine or object method which you want to call but aren't interested in the value returned.If a query is compiled in an edition that is in the usable range of editions for the virtual column, then the optimizer will consider using the index to evaluate the query.
If a query is compiled in an edition outside the usable range of editions for the virtual column, then the optimizer will not consider using the index.
If you know what you're doing with it and you're sure that the variables in question are defined (nor not) as you expect them to be, then you can rely on this feature to implement some powerful "global" data sharing techniques.