Test Your Microsoft SQL Server UNIQUE Constraint Knowledge with This Quiz

Progress

True / False

A UNIQUE constraint ensures that all values in a column are unique.

True False

The UNIQUE constraint ensures that all values in a column or a set of columns are unique.

True / False

A table can have only one UNIQUE constraint.

True False

A table can have multiple UNIQUE constraints on different columns or sets of columns.

True / False

NULL values are allowed in a column with a UNIQUE constraint.

True False

NULL values are allowed in a column with a UNIQUE constraint, but only one NULL is allowed.

True / False

UNIQUE constraints can be applied to multiple columns to enforce uniqueness across the combination of values.

True False

UNIQUE constraints can be applied to a combination of columns to ensure that the combined values are unique.

True / False

UNIQUE constraints automatically create a unique index on the specified column.

True False

UNIQUE constraints create a unique index to enforce the uniqueness of values in the specified column.

True / False

A UNIQUE constraint and a PRIMARY KEY constraint can be applied to the same column.

True False

A column cannot have both a UNIQUE constraint and a PRIMARY KEY constraint, as PRIMARY KEY already ensures uniqueness.

True / False

You can drop a UNIQUE constraint using the ALTER TABLE statement.

True False

The ALTER TABLE statement can be used to drop a UNIQUE constraint from a table.

True / False

UNIQUE constraints can be applied to both character and numeric columns.

True False

UNIQUE constraints can be applied to any data type, including character and numeric columns.

True / False

UNIQUE constraints enforce the uniqueness of values during both INSERT and UPDATE operations.

True False

UNIQUE constraints check for uniqueness during both INSERT and UPDATE operations.

Q10

True / False

UNIQUE constraints can be applied to columns that allow NULL values.

True False

UNIQUE constraints can be applied to columns that allow NULL values, but only one NULL value is allowed.

Q11

True / False

A UNIQUE constraint can be created at the time of table creation or after the table has been created.

True False

A UNIQUE constraint can be added to a table during creation or added later using ALTER TABLE.

Q12

True / False

The UNIQUE constraint can be defined only on a single column in a table.

True False

The UNIQUE constraint can be defined on a single column or a combination of columns in a table.

Q13

True / False

UNIQUE constraints are a type of integrity constraint.

True False

UNIQUE constraints are used to maintain data integrity by ensuring unique values in a column.

Q14

True / False

You cannot disable a UNIQUE constraint temporarily.

True False

UNIQUE constraints can be disabled temporarily using the ALTER TABLE statement.

Q15

True / False

UNIQUE constraints can be enforced at the column level only.

True False

UNIQUE constraints can be enforced at both the column level and the table level.

Q16

Single Choice

What is the main purpose of a UNIQUE constraint in SQL Server?

To enforce referential integrity To ensure all values in a column are unique To limit the length of text in a columnTo prevent NULL values

The main purpose of a UNIQUE constraint is to ensure that all values in a column are unique.

Q17

Single Choice

Which of the following statements about UNIQUE constraints is true?

They can be applied only to numeric columns. They enforce uniqueness only during INSERT operations. They can be applied to multiple columns.They do not allow NULL values.

UNIQUE constraints can be applied to multiple columns to ensure the uniqueness of the combination of values.

Q18

Single Choice

How does a UNIQUE constraint differ from a PRIMARY KEY constraint?

UNIQUE constraints do not allow NULL values. PRIMARY KEY constraints cannot be applied to multiple columns. PRIMARY KEY constraints create non-clustered indexes.PRIMARY KEY uniquely identifies each row, UNIQUE ensures unique values.

A PRIMARY KEY constraint uniquely identifies each row in a table, while a UNIQUE constraint ensures unique values in a column or combination of columns.

Q19

Single Choice

Can a column have both a UNIQUE constraint and a FOREIGN KEY constraint?

Yes, it can. No, it cannot. Only if it is not part of the primary key.Only if it is part of the primary key.

A column can have both a UNIQUE constraint and a FOREIGN KEY constraint.

Q20

Single Choice

What happens if you try to insert a duplicate value into a column with a UNIQUE constraint?

The duplicate value will be inserted. The existing value will be updated. An error will be returned.The duplicate value will be ignored.

Inserting a duplicate value into a column with a UNIQUE constraint will result in an error.

Q21

Single Choice

Can a UNIQUE constraint be defined on a computed column?

Yes, it can. No, it cannot. Only if the column is indexed.Only if the column is non-nullable.

A UNIQUE constraint can be defined on a computed column as long as the computation is deterministic.

Q22

Single Choice

What is the default behavior of a UNIQUE constraint regarding NULL values?

NULL values are not allowed. Only one NULL value is allowed. Multiple NULL values are allowed.NULL values are converted to empty strings.

The default behavior allows one NULL value in a column with a UNIQUE constraint.

Q23

Single Choice

Which SQL statement is used to add a UNIQUE constraint to an existing column?

ALTER TABLE CREATE TABLE UPDATE TABLEINSERT INTO

The ALTER TABLE statement is used to add a UNIQUE constraint to an existing column.

Q24

Single Choice

Can a UNIQUE constraint be defined on a table with no primary key?

Yes, it can. No, it cannot. Only if the table has at least one index.Only if the table is partitioned.

A UNIQUE constraint can be defined on any table, regardless of whether it has a primary key.

Q25

Single Choice

Which of the following is a characteristic of a UNIQUE constraint?

Allows duplicate values Ensures unique values Can be disabled by defaultOnly applies to primary keys

A UNIQUE constraint ensures that no duplicate values are allowed in the specified column(s).

Q26

Single Choice

How can a UNIQUE constraint be removed from a column?

DELETE CONSTRAINT REMOVE CONSTRAINT DROP CONSTRAINTDISABLE CONSTRAINT

A UNIQUE constraint can be removed using the ALTER TABLE statement with the DROP CONSTRAINT clause.

Q27

Single Choice

Can UNIQUE constraints be enforced on the combination of two or more columns?

Yes, they can. No, they cannot. Only on numeric columns.Only on indexed columns.

UNIQUE constraints can enforce the uniqueness of the combination of two or more columns.

Q28

Single Choice

What is the result of applying a UNIQUE constraint to a column that already contains duplicate values?

Duplicates will be automatically removed. An error will occur. The constraint will be ignored.Duplicates will be converted to NULL.

Applying a UNIQUE constraint to a column with duplicate values will result in an error.

Q29

Single Choice

Which constraint ensures that all values in a column or a set of columns are unique?

PRIMARY KEY FOREIGN KEY CHECKUNIQUE

The UNIQUE constraint ensures that all values in a column or a set of columns are unique.

Q30

Single Choice

How many NULL values are allowed in a column with a UNIQUE constraint?

None One TwoUnlimited

Only one NULL value is allowed in a column with a UNIQUE constraint.

Q31

Multiple Choice

Which of the following are characteristics of a UNIQUE constraint?

Ensures all values are unique Allows multiple NULL values Can be defined on multiple columnsCannot be dropped once defined

UNIQUE constraints ensure that all values are unique and allow multiple NULL values.

Q32

Multiple Choice

Which SQL statement can be used to add a UNIQUE constraint?

ALTER TABLE CREATE TABLE INSERT INTOSELECT INTO

The ALTER TABLE and CREATE TABLE statements can be used to add UNIQUE constraints.

Q33

Multiple Choice

What actions can be taken to remove a UNIQUE constraint?

ALTER TABLE DROP CONSTRAINT DELETE FROM REMOVE INDEXALTER TABLE DROP COLUMN

The ALTER TABLE statement with DROP CONSTRAINT can be used to remove UNIQUE constraints.

Q34

Multiple Choice

Which of the following statements are true about composite unique keys?

Involve multiple columns Ensure uniqueness across combinations of values Can be used with non-unique indexesOnly apply to single columns

Composite unique keys involve multiple columns to enforce uniqueness across the combination of values.

Q35

Multiple Choice

Which of the following are limitations of UNIQUE constraints?

Cannot enforce complex data validation Cannot ensure uniqueness across different tables Cannot allow NULL valuesCannot be used with other constraints

UNIQUE constraints cannot enforce complex data validation or ensure uniqueness across different tables.

Q36

Multiple Choice

Which of the following statements are correct about UNIQUE constraints and NULL values?

UNIQUE constraints allow multiple NULL values UNIQUE constraints do not allow NULL values UNIQUE constraints treat NULL as a unique valueUNIQUE constraints require non-null values

UNIQUE constraints allow multiple NULL values since NULL is not considered a value.

Q37

Multiple Choice

Which of the following scenarios would cause a UNIQUE constraint violation?

Inserting duplicate values Inserting NULL values Inserting multiple identical non-null valuesInserting unique non-null values

Inserting duplicate values or multiple identical non-null values would cause a UNIQUE constraint violation.

Q38

Multiple Choice

Which of the following can be used to enforce data integrity?

UNIQUE constraints PRIMARY KEY constraints FOREIGN KEY constraintsCHECK constraints

UNIQUE constraints, PRIMARY KEY constraints, and FOREIGN KEY constraints enforce data integrity.

Q39

Multiple Choice

What are the advantages of using UNIQUE constraints?

Prevent duplicate values Allow multiple NULL values Support indexing for performanceEnsure data consistency

UNIQUE constraints help maintain data integrity by preventing duplicate values and allowing indexing for performance.

Q40

Multiple Choice

Which constraints can be used together to ensure data uniqueness and referential integrity?

UNIQUE constraints PRIMARY KEY constraints FOREIGN KEY constraintsCHECK constraints

Combining UNIQUE constraints with PRIMARY KEY and FOREIGN KEY constraints ensures data uniqueness and referential integrity.

Q41

Multiple Choice

Which of the following are true about indexing with UNIQUE constraints?

Automatically create unique indexes Improve query performance Prevent duplicate index valuesRequire additional storage

UNIQUE constraints automatically create unique indexes, which improve query performance.

Q42

Multiple Choice

What operations can be restricted by UNIQUE constraints?

Insert operations Update operations Delete operationsSelect operations

UNIQUE constraints restrict insert and update operations that would result in duplicate values.

Q43

Multiple Choice

Which of the following are valid reasons to use a UNIQUE constraint?

To ensure data integrity To improve query performance To prevent NULL valuesTo support composite keys

UNIQUE constraints are used to ensure data integrity and improve query performance.

Q44

Multiple Choice

Which constraints can be combined with UNIQUE constraints for comprehensive data validation?

CHECK constraints PRIMARY KEY constraints FOREIGN KEY constraintsDEFAULT constraints

Combining UNIQUE constraints with CHECK, PRIMARY KEY, and FOREIGN KEY constraints provides comprehensive data validation.

Q45

Multiple Choice

Which of the following best describes how UNIQUE constraints handle duplicate values?

Prevent duplicate values Allow duplicate NULL values Require unique non-null valuesAllow duplicate non-null values

UNIQUE constraints prevent duplicate values, ensuring that all values in a column are unique.

Microsoft SQL Server Database Quiz Questions