13 Copyright © Oracle Corporation, All rights reserved. Maintaining Data Integrity

13-2 Copyright © Oracle Corporation, All rights reserved. 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

13-3 Copyright © Oracle Corporation, All rights reserved. Data Integrity Application code Table Data Integrity constraint Database trigger

13-4 Copyright © Oracle Corporation, All rights reserved.

13-5 Copyright © Oracle Corporation, All rights reserved. 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

13-6 Copyright © Oracle Corporation, All rights reserved. Constraint States ENABLE NOVALIDATE Existing dataNew data DISABLE NOVALIDATE DISABLE VALIDATE = = ENABLE VALIDATE

13-7 Copyright © Oracle Corporation, All rights reserved.

13-8 Copyright © Oracle Corporation, All rights reserved. Constraint Checking DML statement Check nondeferred constraints COMMIT Check deferred constraints

13-9 Copyright © Oracle Corporation, All rights reserved. Defining Constraints Immediate or Deferred Use the SET CONSTRAINTS statement to make constraints either DEFERRED or IMMEDIATE. The ALTER SESSION statement also has clauses to SET CONSTRAINTS to DEFERRED or IMMEDIATE.

13-10 Copyright © Oracle Corporation, All rights reserved. Primary and Unique Key Enforcement Is an index available for use? Yes No Yes No Create nonunique index Create unique index Do not use index Use existing index Key enabled? Constraint deferrable? Constraint Deferrable? Is the index nonunique? Yes No/Yes No

13-11 Copyright © Oracle Corporation, All rights reserved. Foreign Key Considerations Appropriate SolutionDesired Action Drop parent table Cascade constraints Truncate parent tableDisable or drop foreign key Perform DML on child tableEnsure that the tablespace containing the parent key is online Use the CASCADE CONSTRAINTS clause Drop tablespace containing parent table

13-12 Copyright © Oracle Corporation, All rights reserved.

13-13 Copyright © Oracle Corporation, All rights reserved. Defining Constraints While Creating a Table CREATE TABLE hr.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 users;

13-14 Copyright © Oracle Corporation, All rights reserved.

13-15 Copyright © Oracle Corporation, All rights reserved.

13-16 Copyright © Oracle Corporation, All rights reserved.

13-17 Copyright © Oracle Corporation, All rights reserved. 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 the initial load. –Defer constraint checking.

13-18 Copyright © Oracle Corporation, All rights reserved. Enabling Constraints No locks on table Primary and unique keys must use nonunique indexes ENABLE NOVALIDATE ALTER TABLE hr.departments ENABLE NOVALIDATE CONSTRAINT dept_pk;

13-19 Copyright © Oracle Corporation, All rights reserved.

13-20 Copyright © Oracle Corporation, All rights reserved.

13-21 Copyright © Oracle Corporation, All rights reserved. Enabling Constraints Locks the table Can use unique or nonunique indexes Needs valid table data ENABLE VALIDATE ALTER TABLE hr.employees ENABLE VALIDATE CONSTRAINT emp_dept_fk;

13-22 Copyright © Oracle Corporation, All rights reserved.

13-23 Copyright © Oracle Corporation, All rights reserved. Using the EXCEPTIONS Table Create the EXCEPTIONS table by running the utlexcpt1.sql script. Execute the ALTER TABLE statement with EXCEPTIONS option. Use subquery on EXCEPTIONS to locate rows with invalid data. Rectify the errors. Reexecute ALTER TABLE to enable the constraint.

13-24 Copyright © Oracle Corporation, All rights reserved.

13-25 Copyright © Oracle Corporation, All rights reserved.

13-26 Copyright © Oracle Corporation, All rights reserved. Obtaining Constraint Information Obtain information about constraints by querying the following views: DBA_CONSTRAINTS DBA_CONS_COLUMNS

13-27 Copyright © Oracle Corporation, All rights reserved.

13-28 Copyright © Oracle Corporation, All rights reserved.

13-29 Copyright © Oracle Corporation, All rights reserved. Summary In this lesson, you should have learned how to: Implement data integrity Use an appropriate strategy to create and maintain constraints Obtain information from the data dictionary

13-30 Copyright © Oracle Corporation, All rights reserved. Practice 13 Overview This practice covers the following topics: Creating constraints Enabling unique constraints Creating an EXCEPTIONS table Identifying existing constraint violations in a table, correcting the errors, and reenabling the constraints

13-31 Copyright © Oracle Corporation, All rights reserved.

13-32 Copyright © Oracle Corporation, All rights reserved.