Oracle Database SQL — Question 61

Which two are true about constraints? (Choose two.)

Answer options

• A. A column with a FOREIGN KEY constraint can never contain a NULL value.
• B. A constraint can be disabled even if the constrained column contains data.
• C. Constraints are enforced only during INSERT operations.
• D. All constraints can be defined at the table or column level.
• E. A column with a UNIQUE constraint can contain a NULL value.

Correct answer: B

Explanation

Option B is correct because constraints can indeed be disabled regardless of whether there is existing data in the constrained column. Option A is incorrect because a FOREIGN KEY constraint can allow NULL values. Option C is wrong since constraints are enforced during both INSERT and UPDATE operations. Option D is not entirely accurate as certain constraints are more typically defined at the table level. Option E is also true, but it does not pertain to the correct answer for this question.