Hi Friends,
Let's give a brief light on Constraints
Let's give a brief light on Constraints
Constraint:- It is the rule which
restrict the incorrect data to be inserted into the database.
Types of Constraint:-
1.
Not
Null Constraint
2.
Unique Constraint
3.
Check Constraint
4.
Primary
Key Constraint
5.
Foreign
Key Constraint
6.
Ref
Key(Referential Kay) Constraint
TABLE LEVEL CONSTRAINT:-
COLUMN LEVEL CONSTRAINT:-
1. NOT
NULL:-This is the constraints will avoid null values to the column specified.
NOTE:-
It is the only constraint cannot be
defined at Table level.
Syntax:-Create table <table_name>
(Empno NUMBER Constraint Empno_NN NOT NULL,
ENAME VARCHAR2(30) NOT NULL
);
SQL> create table emp_info
2 (
3
empno number Constraint empno_pk Primary key,
4
ename varchar2(20) Not Null,
5 Job
varchar2(20) Constraint job_NN Not
Null,
6 MGR
NUMBER Constraint mgr_ref References emp_info(empno),
7
HIREDATE Date,
8 Sal
Number Constraint sal_chk CHECK (sal Between 500 and 5500),
9
comm Number,
10
Deptno Number,
11
Constraint deptno_fk FOREIGN KEY(deptno) References dept(deptno)
12 );
Data
Dictionary:-User_Constraints , User_cons_columns
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