Which SQL constraint ensures that all values in a column are unique?OptionsDEFAULTUNIQUEPRIMARY KEYCHECK

Understanding the Question

The question asks about an SQL constraint that guarantees that all values in a specific column of a database table are unique.

Analyzing the Options

1. DEFAULT: This constraint provides a default value for a column when no value is specified. It does not enforce uniqueness.

2. UNIQUE: This constraint ensures that all values in a column are distinct from one another, preventing duplicate entries.

3. PRIMARY KEY: This constraint also ensures uniqueness, as it uniquely identifies each record in a table. However, a primary key can only be defined once per table.

4. CHECK: This constraint is used to limit the values that can be entered into a column based on a specific condition but does not enforce uniqueness.

Conclusion

The correct answer is UNIQUE. This constraint is specifically designed to ensure that all values in a column are unique across all records in a table.