![Business Rules(contd.) TRIGGERS FORMAT Create [or replace] trigger <trigger_name> [enable|disable] <before|after> <insert|update|delete> [of <column_name_list>] On <table_name> [referencing new as <synonym>] [for each row] [when (trigger_condition)] <trigger_code>](https://image.slidesharecdn.com/dataintegrity-110919030447-phpapp02/85/Data-integrity-41-320.jpg)
Data integrity
- 1. Data Integrity Chapter 11
- 2. Definition Correctness and completeness of data in a database
- 3. When is data integrity lost? Invalid data added to the database Existing data modified to incorrect value Changes to database lost Changes partially applied
- 4. How is data integrity preserved? Through Data Integrity Constraints Constraints restrict data values that can be inserted or updated
- 5. Types of Data Integrity Constraints Required Data:Columns must contain valid data value in every row,NOT NULL Validity Checking:Columns must contain data within the domain,set of values legal for a column-data type,CHECK,Domain Entity Integrity:Primary key must contain unique value in each row
- 6. Types of Data Integrity Constraints(contd.) Referential Integrity:Foreign Key linking each row of child table to matching primary key value in parent table Other data relationships:additional constraints governing legal data values Business Rules Consistency:Multiple updates involving many tables may make database inconsistent
- 7. Required data NOT NULL constraint in CREATE TABLE statement Ensures that each INSERT statement specifies a non null value (Error for null) Ensures that each UPDATE statement specifies a non null value (Error for null) Must be specified at table creation time Adding NOT NULL constraint after data values are added may result in error if any null values found for the column
- 8. Validity Checking Data type ensures specific values of a type to be present for the column Two features to support validity checking-column check constraints and domains
- 9. Validity Checking (contd.) Column CHECK constraints – Search condition that produces true/false values Specified with CREATE TABLE With the CHECK constraint ,DBMS checks value of that column each time a new row is inserted or updated Allows if condition true Error if condition false
- 10. Validity Checking(contd.) CHECK CONSTRAINT EXAMPLE Create table test (rollno number(2) check (rollno between 1 and 80), name varchar2(15) ); Insert into test values(55,’ANANYA’); 1 row inserted Insert into test values(85,’AKSHAT’); ERROR-Check constraint violated
- 11. Validity Checking(contd.) Domains (SQL2) Generalizes CHECK Constraint Same CHECK constraint can be applied to many different columns within a database through DOMAIN-a collection of legal data values Domain defined with a name and a search condition for range of legal data values CREATE DOMAIN statement
- 12. Validity Checking(contd.) Domain example Create DOMAIN dom_val_bet number(2) CHECK (value between 1 and 60); Create TABLE test1 (rollno dom_val_bet, name varchar2(15) ); Create table test2 (rollno dom_val_bet, marks number(3) );
- 13. Validity Checking(contd.) Why use DOMAIN??? Can be used repeatedly simplifying table definitions Changing definition later, if required becomes easy Specially helpful for large databases
- 14. Entity Integrity Each entity is unique Table’s PRIMARY KEY must have unique values for each row DBMS automatically checks uniqueness of primary key value for each insert or update Insert or update to include duplicate value in primary key column results in error If required for non-primary key column,UNIQUE constraint or CREATE INDEX Uniqueness also enforces NOT NULL for primary key
- 15. Referential Integrity Foreign key-primary key relationship Each foreign key value in child table must have a corresponding value in primary key column of parent table Ensures integrity of parent-child relationship in tables
- 16. Referential Integrity Problems Inserting a new child row Updating the foreign key in a child row Deleting a parent row Updating the primary key in a parent row
- 17. Delete and Update Rules Delete Rules Restrict delete rule(default) -prevents deletion of a row with children Cascade delete rule -when parent row deleted all child rows automatically deleted Set null delete rule – when parent row deleted foreign key values of all child rows set to null Set default delete rule - when parent row deleted foreign key values of all child rows set to default value set for that column What to do when User tries to delete a row of parent table?
- 18. Delete and Update Rules Update Rules Restrict update rule(default) -prevents updation of a row with children Cascade update rule -when parent row updated all child rows automatically updated accordingly Set null update rule – when parent row updated foreign key values of all child rows set to null Set default delete rule - when parent row updated foreign key values of all child rows set to default value set for that column What to do when User tries to update a row of parent table?
- 19. Cascaded deletes and Updates Restrict is a single level rule Set Null and Set Default are two level rules Cascade can be a multi level rule Cascade delete rules must be used with special care as it may cause widespread deletion if used incorrectly Cascade update affects more only if foreign key of child table is also its primary key
- 20. Referential Cycles When a child table’s primary key is referred by a column of the parent’s table a referential cycle is formed. Dept Emp Deptno Dname loc mgr Empno Ename dob sal deptno comm
- 21. Referential cycles (contd.) Inserting a row in EMP table not allowed as there must be corresponding deptno value in DEPT table . Inserting a row in DEPT table not allowed as there must be corresponding value for mgr in EMP(empno) Only possible when mgr is allowed null value Sometimes it is convenient if constraints are not checked immediately-deferred checking In referential cycles cascade delete rule should be given very cautiously
- 22. Foreign Keys and Null Values Allowed to have Null values For handling Null values in foreign key columns options provided in CREATE TABLE statement: Match Full :foreign keys in child table fully match primary key in parent table Match Partial :Allows null values in parts of the foreign key,non-null values match the corresponding parts of primary key in parent table
- 23. Advanced Constraint Capabilities FOUR types of Constraints Column Constraints: appear in individual column definitions in CREATE TABLE statement eg. CREATE TABLE TEST2 ( ROLLNO NUMBER PRIMARY KEY, NAME VARCHAR2(15) );
- 24. Advanced Constraint Capabilities (contd.) Domains: specialized type of column constraint Provide capability to define new data types Predefined data type + additional constraints once created,can be used in place of data type Defined outside the table with CREATE DOMAIN statement
- 25. Advanced Constraint Capabilities (contd.) Table Constraints:usually appear as a group after column definitions Eg. Create table offices ( office number(5) not null , city varchar2(15), mgr number(4), primary key(office), foreign key(mgr) references salesreps(empno) on delete set null, unique(city) );
- 26. Advanced Constraint Capabilities (contd.) Assertions Specified outside table definition Specifies relationship between data values crossing multiple tables Create large database processing overhead so defined with care Eg. Create assertion cr_ord check(customer.credit_limit<= select sum(orders.amount) from orders where orders.cust=customer.cust_num);
- 27. SQL2 Constraint Types 1. NOT NULL Prevents null values Column constraint
- 28. SQL2 Constraint Types (contd.) PRIMARY KEY unique and not null Can be a column or a table constraint When a single column,column constraint is convenient When on multiple columns, table constraint must
- 29. SQL2 Constraint Types(contd.) UNIQUE Column or table constraint When for a single column,column constraint is convenient When on combination of multiple columns, table constraint must
- 30. SQL2 Constraint Types (contd.) 4. Referential Integrity (Foreign Key) Constraint Column or table constraint When for a single column,column constraint is convenient When on combination of multiple columns, table constraint must When many foreign key relationships to many tables, convenient to gather all together as table constraint
- 31. SQL2 Constraint Types (contd.) 5. Check Constraint Column or table constraint Only constraint that forms part of domain and assertion definition Specified as search condition Constraint satisfied if condition returns true
- 32. SQL2 Constraint Types (contd.) For small databases constraint names not necessary For larger databases ,constraint names must be given CHECK constraint in an assertion must have a name
- 33. Deferred Constraint Checking Constraints are checked with every insert , update and delete Deferred constraint checking allows checking constraints at the completion of a transaction(COMMIT) Useful when several updates required at once to keep database consistent
- 34. Deferred Constraint Checking(contd.) At the time of constraint creation two options: DEFERRABLE: checking can be deferred to the end of the transaction NOT DEFERRABLE (default): checking cannot be deferred.
- 35. Deferred Constraint Checking(contd.) For DEFERRABLE: Initially Immediate (default): starts out as an immediate constraint Initially Deferred :starts out as a deferred constraint Create assertion quota_totals Check ((offices.quota=sum(salesreps.quota)) and (salesreps.rep_office=offices.office)) deferrable initially immediate;
- 36. Deferred Constraint Checking(contd.) SET CONSTRAINTS SET CONSTRAINTS :to control the immediate or deferred processing of constraints Set constraints quota_totals deferred Insert……….. Delete……….. Commit Insert………….. Initially the constraint will not be checked for first insert and delete statements,changes will be checked at commit and quota_totals again is set to deferrable initially immediate. Second insert statement would be checked immediately
- 37. Business Rules Manager to be notified whenever a customer is assigned a credit limit of more than Rs.1 lakh Manager to be notified whenever a Sales Representative finishes quota assigned When a new order is taken Qty_in_hand is to be decreased by the quantity ordered DBMS responsible for storing,organizing data,ensuring data integrity.Enforcing business rules is the responsibility of application programs accessing the database.
- 38. Business Rules(contd.) Duplication of effort Lack of consistency Maintenance problems Complexity Disadvantages of application programs enforcing business rules Triggers help DBMS in enforcing business rules
- 39. Business Rules(contd.) TRIGGERS For any event that causes a change in the database , user can specify an action to be carried out by DBMS using a trigger Events that can trigger an action are insert, update and delete Action triggered by the event is a sequence of SQL statements
- 40. Business Rules(contd.) TRIGGERS Create trigger top_stud_trig after insert on student referencing new as newstud when (marks>95) insert into highrankers values(newstud.rollno,marks) for each row Inserting records in separate highrankers table when marks >95
- 41. Business Rules(contd.) TRIGGERS FORMAT Create [or replace] trigger <trigger_name> [enable|disable] <before|after> <insert|update|delete> [of <column_name_list>] On <table_name> [referencing new as <synonym>] [for each row] [when (trigger_condition)] <trigger_code>
- 42. Business Rules(contd.) TRIGGERS - Advantages Help in enforcing business rules Useful for enforcing referential integrity If new data is inconsistent an error can be raised to rollback the entire transaction
- 43. Business Rules(contd.) TRIGGERS - Disadvantages Database complexity increases Hidden rules Hidden performance implications
- 44. THANKS