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If you choose not to use NULL values, you??™re forcing a value to be assigned to a column
for every row. Youare, in effect, eliminating the possibility of having a column that
doesn??™t require a value, as well as potentially assigning misleading values for certain
columns. This situation can be misleading for end users and can lead to inaccurate
results for summary actions such as AVG (average).
Avoiding NULL values simply replaces one problem??”educating users or providing
them with an interface that implicitly understands NULL values??”with another set of
problems, which can lead to a loss of data integrity.
Basic Data Structures | 91
is read-only; youcannot update the data it contains. The external table is good for
loading and unloading data to files from a database, among other purposes.
Oracle Database 11g introduces the ability to create virtual columns for a table.
These columns are defined by an expression and, although the results of the expression
are not stored, the columns can be accessed by applications at runtime.


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