If A is a foreign key in R, no null values are permitted in the column A in any instance of R. True False
Question
If A is a foreign key in R, no null values are permitted in the column A in any instance of R. True False
Solution
False. A foreign key in a relation R can have null values. The only constraint is that if the value is not null, then it must match a value in the primary key of the table that the foreign key references.
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