Index. Defination of Constraint Column level Table level Data Constraint A Different Constraint

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1 Index Defination of Constraint Column level Table level Data Constraint A Different Constraint I. Primary Key Constraint II. Foreign Key Constraint III. Check Constraint IV. Not Null Constraint

2 Defination of Data constraint: A Constraint is condition or check applicable on a field or set of fields. A constraints can either be placed at :- 1. Column level 2. Table level

3 Column level:- A Constraint given at the column level is called as Column level. It defines a rule for a single column. Example is PRIMARY KEY constraint when a single column is the primary key of the table. Table level:- A constraint given at the table level is called as Table level. It may refer to more than one column of the table. Example is PRIMARY KEY constraint that is used to define composite primary key.

4 DATA CONSTRAINTS All business of the world run on a business data being gathered, stored and analysed. Business manager determine aspect of business rule that must be applied to the data prior to it being stored in the database such rules have been enforced to database. Only data which satisfy the condition set, should be stored for future analysis. If the condition set, it must be rejected. This ensure that the data stored in a table will be valid.

5 A Different Constraints:- 1 } Primary Key Constraint 2} Foreign / Secondary Key Constraint 3} Check Constraint 4} Not Null Constraints

6 PRIMARY KEY CONSTRAINT As a result it is used to identify a row & avoids duplication of rows. It does not allow Null values. A table can have only one primary key. If a primary key constraint is assigned to combination of columns it is said to be 'composite primary key or a multicolumn primary key is called a Composite primary key. It is the Type of Entity Integrity Constraint.

7 Primary key as a column Level:- Syntax:- (<Column name><datatype>(<size>)primary key EX: Create client_master where client_no is the Primary key. CREATE TABLE client_master (client_no varchar2(6) PRIMARY KEY, name varchar2(20), address varchar2(15), city varchar2(15), state varchar2(15), pincode number(6));

8 Primary Key as Table Level :- Syntax: PRIMARY KEY(<col1>,<col2> ); Q:Create a sales_order_details table where CREEATE TABLE sales _order_details (s_order_no varchar2(6), Product_no varchar2(6), Qty_orderd number(8,2), qty_disp number(8), product_rate number(8,2), PRIMARY KEY(s_order_no,product_no));

9 FOREIGN KEY CONSTRAINT Foreign key represent relationship between tables. A Foreign key is a column whose values are derived from the primary key of the same or some other table. The Table I which the foreign key is defined is called a foreign table or detailed table the table that defines The Primary key & is referenced by the foreign key is called as Primary table or master table.

10 Foreign Key as column level: Syntax:- (colname)<datatype>(size)references <table name>[<colname>] EX: Consider 2 tables EMPLOYEE and DEPARTMENT which are related with one another as,

11 1] CREATE TABLE DEPT (Dept_number(3)PRIMARY KEY, Dept_name varchar2(20), Location varchar2(20)); 2] CREATE TABLE EMPLOYEE (emp_no number(4) PRIMARY KEY, emp_name varchar2(25), date_of_join date, salary number(8,2), dept_no number(3)references dept(dept_no));

12 Foreign Key as table Level:- Syntax: FOREIGN KEY(<colname>,<colname> ) REFERENCES<tablename*<colname><colname +; EX: CREATE TABLE sales_order_details( order_no number(6), item_no number(6), qty_orderd number(8,2), PRIMARY KEY (order_no,item_no), FOREIGN KEY(order_no), REFERECES sales_order);

13 CHECK CONSTRINT Check constraint must be specified as a logical expression that evaluates either to true or false. A check constraint must be avoided if the constraint can be defined using primary key or foreign key,not null constraint. Data values being inserted into the column client_no must with the capital letter C. Only allow Pune, Mumbai,madras legal values for the column city. Check constraint it is the type of Domain integrity constraints.

14 Check Level as column level. Syntax:- <colname><datatype>(size)check(<logical expression>) EX: Create table client_master (client_no varchar2(6)constraint ck_clientno CHECK(client_no like C% ), name varchar2(20)constraint ck_cname CHECK(name=upper(name)), address varchar2(15), city varchar2(10) CONSTRAINT ck_city (city IN( mumbai, Pune, Madras )), state varchar2(20),pincode number(6));

15 NOT NULL When column define as NOT NULL then that column become NOT EMPTY column. A null value is not equivalent to value of 0. If the datatype is number & is not equivalent to spaces if the datatype is character.

16 Syntax:- <colname><datatype>(<size>)not NULL EX: Create table vender_master (vencode varchar2(5), venname varchar2(25)not null, tel_no number(6));