Database Objects and Constraints Flashcards

Which Oracle constraint ensures that a column value cannot be NULL?

Answer: NOT NULL

The NOT NULL constraint prevents a column from accepting NULL values, ensuring every row has a value for that column.

Which constraint ensures that each value in a column is unique across the table but still allows NULL values?

Answer: UNIQUE

The UNIQUE constraint ensures no two rows have the same non-NULL value in the constrained column, but unlike PRIMARY KEY, it permits NULL values.

What is the primary purpose of a FOREIGN KEY constraint in Oracle Database?

Answer: To enforce referential integrity between two tables

A FOREIGN KEY constraint enforces referential integrity by ensuring values in the child table's column match existing values in the referenced parent table's primary key.

Which constraint type allows you to specify a condition that every row's column value must satisfy?

Answer: CHECK

The CHECK constraint defines a condition that must evaluate to TRUE for every row, letting you restrict which values are accepted in a column.

Which statement about the PRIMARY KEY constraint is correct?

Answer: A PRIMARY KEY uniquely identifies each row and does not allow NULLs

A PRIMARY KEY constraint combines NOT NULL and UNIQUE, ensuring the primary key column(s) uniquely identify each row and contain no NULL values.

What is a composite primary key in Oracle Database?

Answer: A primary key made up of two or more columns

A composite primary key consists of two or more columns whose combined values must be unique across all rows in the table.

When a FOREIGN KEY constraint with ON DELETE CASCADE is defined, what happens when a parent row is deleted?

Answer: The child rows are automatically deleted

ON DELETE CASCADE causes Oracle to automatically delete all child rows that reference the deleted parent row, propagating the deletion down the relationship.