Section 14
Foreign Key Constraints are
also known as:
Parental
Key Constraints
Child
Key Constraints
Multi-Table
Constraints
Referential
Integrity Constraints (*)
Which line of the following
code will cause an error:
CREATE TABLE clients
(client_number NUMBER(4) CONSTRAINT client_client_num_pk
PRIMARY KEY,
first_name VARCHAR2(14),
last_name VARCHAR2(13),
hire_date DATE CONSTRAINT emp_min_hire_date CHECK (hire_date
< SYSDATE),
department_id NUMBER(4),
CONSTRAINT clients_dept_id_fk FOREIGN KEY(department_id)
REFERENCES departments(department_id));
Line 2
Line 3
Line 5
(*)
Line 7
If a Primary Key is made up of
more than one column, one of the columns can be null. True or False?
True
False
(*)
Which of the following best
describes the function of a CHECK constraint?
A CHECK
constraint defines restrictions on the values that can be entered in a column
or combination of columns. (*)
A CHECK
constraint is created automatically when a PRIMARY KEY constraint is created.
A CHECK
constraint enforces referential data integrity.
A CHECK
constraint enforces uniqueness of the values that can be entered in a column or
combination of columns.
A composite primary key may
only be defined at the table level. True or False?
True
(*)
False
A table must have at least one not null constraint and one
unique constraint. True or False?
True
False
(*)
Which of the following is not a
valid Oracle constraint type?
EXTERNAL
KEY (*)
UNIQUE
KEY
PRIMARY
KEY
NOT
NULL
If the employees table has a
UNIQUE constraint on the DEPARTMENT_ID column, we can only have one employee
per department. True or False?
True
(*)
False
Evaluate this CREATE TABLE
statement:
CREATE TABLE customers
(customer_id
NUMBER,
customer_name
VARCHAR2(25),
address
VARCHAR2(25),
city
VARCHAR2(25),
region
VARCHAR2(25),
postal_code
VARCHAR2(11),
CONSTRAINT
customer_id_un UNIQUE(customer_id),
CONSTRAINT
customer_name_nn NOT NULL(customer_name));
Why does this statement fail when executed?
NOT
NULL constraints CANNOT be defined at the table level. (*)
The
NUMBER data types require precision values.
The
CREATE TABLE statement does NOT define a PRIMARY KEY.
UNIQUE
constraints must be defined at the column level.
A column defined as NOT NULL can
have a DEFAULT value of NULL. True or False?
True
False
(*)
This SQL command will do what?
ALTER TABLE employees
ADD CONSTRAINT emp_manager_fk FOREIGN KEY(manager_id)
REFERENCES employees(employee_id);
Add a
FOREIGN KEY constraint to the EMPLOYEES table restricting manager ID to match
every employee ID.
Add a
FOREIGN KEY constraint to the EMPLOYEES table indicating that a manager must
already be an employee. (*)
Alter
table employees and add a FOREIGN KEY constraint that indicates each employee
ID must be unique.
Alter
the table employees and disable the emp_manager_fk constraint.
Once constraints have been
created on a table, you will have to live with them as they are unless you drop
and re-create the table. True or False?
True
False
(*)
You can drop a column in a table
with a simple ALTER TABLE DROP COLUMN statement, even if the column is
referenced in a constraint. True or False?
True
False
(*)
What mechamisn does Oracle use in
the background to enforce uniqueness in Primary and Unique key constraints?
Internal
Pointers
Nothing
extra is created when Primary Keys and Unique Keys are created
Ordered
Lists
Unique
key indexes are created in the background by Oracle when Primary key and Unique
key constraints are created or enabled (*)
Evaluate this statement:
ALTER TABLE employees
ADD CONSTRAINT employee_id PRIMARY KEY;
Which result will the statement provide?
An
existing constraint on the EMPLOYEES table will be enabled.
A
syntax error will be returned. (*)
A
constraint will be added to the EMPLOYEES table.
An
existing constraint on the EMPLOYEES table will be overwritten.
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