SQL Quiz

In an entity-relationship diagram, what is the purpose of a weak entity?

• To represent an entity that does not have its own unique identifier.

• To represent an entity that has a one-to-one relationship with another entity.

• To represent an entity that has a many-to-many relationship with another entity.

What is the purpose of the CASCADE DELETE constraint in SQL?

• To automatically delete all related records when a record is deleted.

• To prevent the deletion of a record if it is referenced by other records.

• To update the foreign key values when a record is deleted.

What is the purpose of the EXISTS operator in SQL?

• To check if a subquery returns any rows.

• To perform calculations on the retrieved data.

• To retrieve data based on the result of another query.

How can a self-referencing relationship be implemented in a relational database?

• By creating a separate table that includes the primary key of the entity.

• By adding a foreign key column in the entity's table that references its own primary key.

• By duplicating the data in the entity's table.

What is the purpose of the HAVING clause in SQL?

• To filter rows based on a specific condition.

• To sort rows in ascending or descending order.

• To filter groups based on a specific condition.

What is the purpose of the TRUNCATE TABLE command in SQL?

• To modify the structure of an existing table.

• To insert new rows into a table.

• To delete all rows from a table.

How can the JOIN operation be used in SQL?

• To combine rows from two or more tables based on a related column between them.

• To update existing data in a table.

• To delete rows from a table.

What is the purpose of the INDEX in SQL?

• To define a constraint on a table.

• To store temporary data that can be accessed later.

• To improve the performance of data retrieval operations.

What is the purpose of the UNION operator in SQL?

• To combine the results of two or more SELECT statements into a single result set.

• To perform calculations on the retrieved data.

• To retrieve data based on the result of another query.

How can the UNION operator be used in SQL?

• To combine the results of two or more SELECT statements into a single result set.

• To perform calculations on the retrieved data.

• To retrieve data based on the result of another query.