1. Maintaining Data Integrity

2. Objectives
After completing this lesson, you should be able to
do the following:
• Implement data integrity constraints
• Maintain integrity constraints
• Obtain constraint information from the data
dictionary

3. Data Integrity
3
Application
code
Integrity
constraint
Database
trigger
Table
Data

4. Types of Constraints
Constraint
NOT NULL
UNIQUE
PRIMARY KEY
FOREIGN KEY
CHECK
Description
Specifies that a column cannot contain null
values
Designates a column or combination of
columns as unique
Designates a column or combination of
columns as the table’s primary key
Designates a column or combination of
columns as the foreign key in a referential
integrity constraint
Specifies a condition that each row of the
table must satisfy

5. Constraint States
Enabled
novalidate
Enabled
validate
Existing dataNew data
Disabled
novalidate
Disabled
validate
=
=

6. Deferred Constraints
DML statement
Check nondeferred
constraints
COMMIT
Check deferred
constraints

7. Defining Constraints as
Immediate or Deferred
Use the command ALTER SESSION or SET
CONSTRAINTS to set the mode for your constraint.
ALTER SESSION
SET CONSTRAINT[S] =
{IMMEDIATE|DEFERRED|DEFAULT};

8. Primary and Unique Key Enforcement
Is an index
available
for use?
Yes
No
No
Yes
Yes
No
Create nonunique
index
Create unique
index
Do not use
index
Use existing
index
Key enabled?
Constraint
deferrable?

9. Foreign Key Considerations
Desired Action
Drop parent table
Truncate parent table
Drop tablespace
containing parent table
Avoid locks on child
table while performing
DML on parent table
Perform DML on child
table
Appropiate Solution
Cascade constraints
Disable or drop foreign key
Use CASCADE CONSTRAINTS
clause
Create index on foreign key
Ensure tablespace containing
parent key index online

10. Defining Constraints While
Creating a Table
CREATE TABLE summit.employee(
id NUMBER(7)
CONSTRAINT employee_id_pk PRIMARY KEY
DEFERRABLE
USING INDEX
STORAGE(INITIAL 100K NEXT 100K)
TABLESPACE indx,
last_name VARCHAR2(25)
CONSTRAINT employee_last_name_nn NOT NULL,
dept_id NUMBER(7))
TABLESPACE data;

11. Guidelines for
Defining Constraints
• Primary and unique constraints:
– Place indexes in a separate tablespace
– Use nonunique indexes if bulk loads are
frequent
• Self-referencing foreign keys:
– Define or enable foreign keys after initial load
– Defer constraint checking

12. Enabling Constraints
• No locks on table
• Primary and unique keys
must use nonunique indexes
Enable
NOVALIDATE
ALTER TABLE summit.department
ENABLE NOVALIDATE CONSTRAINT dept_pk;

13. Enabling Constraints
• Locks table
• Can use unique or nonunique
indexes
• Needs valid table data
Enable
VALIDATE
ALTER TABLE summit.employee
ENABLE VALIDATE CONSTRAINT emp_dept_fk;

14. Using the EXCEPTIONS Table
1. Create EXCEPTIONS table (utlexcpt.sql).
2. Execute ALTER TABLE with EXCEPTIONS clause.
3. Use subquery on EXCEPTIONS to locate rows
with invalid data.
4. Rectify the errors.
5. Reexecute ALTER TABLE to enable the
constraint.

15. Dropping Constraints
• Drop constraints using this command:
• Drop a table and any referencing foreign key using
this command:
ALTER TABLE summit.employee
DROP CONSTRAINT emp_ln_uk;
DROP TABLE department
CASCADE CONSTRAINTS;

16. Getting Constraint Information
DBA_CONSTRAINTS
OWNER
CONSTRAINT_NAME
CONSTRAINT_TYPE
TABLE_NAME
SEARCH_CONDITION
R_OWNER
R_CONSTRAINT_NAME
DELETE_RULE
STATUS
DEFERRABLE
DEFERRED
VALIDATED
GENERATED
BAD
RELY
LAST_CHANGE
DBA_CONS_COLUMNS
OWNER
CONSTRAINT_NAME
TABLE_NAME
COLUMN_NAME
POSITION

17. Summary
In this lesson, you should have learned how to:
• Implement data integrity
• Use an appropriate strategy for creating and
maintaining constraints
• Obtain information from the data dictionary