The statement is true. The vertical subset of a table is produced by the SELECT operator. One table is subtracted from another using the DIFFERENCE operator.
When a value is missing, it is represented by a NULL value, which often has one of three meanings: The amount is unknown (value exists but is not known) Unavailable value (exists but is purposely withheld) Not relevant to the attribute (undefined for this tuple). Column/Attribute refers to the Table's vertical subset. The attributes of a relation in a database are as follows: A relation's values are all atomic, meaning they cannot be subdivided further. OODB, or object-oriented database a database type that supports modern programming languages like C++ and Java by storing data as objects.
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