1Z0-006 Database Objects and Constraints 1 — Questions and Answers
Question 1: Which Oracle constraint ensures that a column value cannot be NULL?
- NOT NULL (Correct answer)
- UNIQUE
- CHECK
- DEFAULT
Correct answer: NOT NULL
The NOT NULL constraint prevents a column from accepting NULL values, ensuring every row has a value for that column.
Question 2: Which constraint ensures that each value in a column is unique across the table but still allows NULL values?
- PRIMARY KEY
- NOT NULL
- UNIQUE (Correct answer)
- CHECK
Correct 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.
Question 3: What is the primary purpose of a FOREIGN KEY constraint in Oracle Database?
- To ensure all values are distinct within a column
- To enforce referential integrity between two tables (Correct answer)
- To limit the range of values in a column
- To prevent NULL values in a column
Correct 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.
Question 4: Which constraint type allows you to specify a condition that every row's column value must satisfy?
- NOT NULL
- UNIQUE
- FOREIGN KEY
- CHECK (Correct answer)
Correct 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.
Question 5: Which statement about the PRIMARY KEY constraint is correct?
- A table can have multiple PRIMARY KEY constraints
- PRIMARY KEY columns allow NULL values
- A PRIMARY KEY uniquely identifies each row and does not allow NULLs (Correct answer)
- PRIMARY KEY constraints can only be defined at the column level
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.
Question 6: What is a composite primary key in Oracle Database?
- A primary key that references multiple tables
- A primary key made up of two or more columns (Correct answer)
- A primary key that allows NULL values in one column
- A primary key created automatically by Oracle
Correct 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.
Question 7: When a FOREIGN KEY constraint with ON DELETE CASCADE is defined, what happens when a parent row is deleted?
- The deletion is rejected if child rows exist
- The child rows are set to NULL
- The child rows are automatically deleted (Correct answer)
- The child rows are moved to an archive table
Correct 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.
1Z0-006 Database Objects and Constraints 1
Which Oracle constraint ensures that a column value cannot be NULL?