In a nonpadded
comparison, the second string would be identified as smaller because it is shorter
than the first string. Nonpadded comparisons are used for comparisons in which one
or both of the values are VARCHAR2 or NVARCHAR2 datatypes, while blankpadded
comparisons are used when neither of the values is one of these datatypes.
Oracle Database 10g and later releases include a feature called the Expression Filter,
which allows youto store a complex comparison expression as part of a row. You
can use the EVALUATE function to limit queries based on the evaluation of the
expression. The Expression Filter uses regular expressions, which are described later
in this chapter.
NULLs
The NULL value is one of the key features of the relational database. The NULL, in
fact, doesn??™t represent any value at all??”it represents the lack of a value. When you
create a column for a table that must have a value, you specify it as NOT NULL,
meaning that it cannot contain a NULL value. If you try to write a row to a database
table that doesn??™t assign a value to a NOT NULL column, Oracle will return an
error.
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