Which of the following are considered as constraints?Select one or more:a.Checkb.NULLc.NOT NULLd.Unique

To answer the question regarding which options are considered as constraints in a database context, we'll analyze each option:

1. Check: This is a constraint that allows you to specify a condition on a column. It ensures that all values in a column satisfy a specific condition. Therefore, this is considered a constraint.

2. NULL: This option isn't a constraint itself but more of a property of a column. It determines whether or not a column can hold NULL values but does not enforce any rules beyond that.

3. NOT NULL: This is a constraint that ensures a column cannot contain NULL values. It enforces that a value must be entered into that column, thus it is considered a constraint.

4. Unique: This is a constraint that ensures all values in a column (or a set of columns) are different. No duplicate values are allowed, so it is also considered a constraint.

Conclusion:

The options considered as constraints are:

• a. Check
• c. NOT NULL
• d. Unique

Final Answer: a. Check, c. NOT NULL, d. Unique