Dear Friends Let's understand the rule of constraints in oracle. 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. 2.    UNIQUE CONSTRAINT:- This is the constraint which will avoid duplicate values to the column specified. It can be specified at column level as well as table level.  3.    CHECK CONSTRAINT:-This is the constraint which will be used for setting few conditions on the specific column. Even this can be defined at table and column level. 4. Primary Key Constraint:-This is the cons

Dear Friend As I stated in my previous blog, Let's start with our first item(SQL). Let's Focus on the   Basic understanding of DBMS and RDBMS and Database and its Architecture What is Data:- The data is stored representation of objects and events which has the meaning .It can be structured or unstructured. What is Information :-It is the data in the processed form which will increase the knowledge of end user. What is Metadata:- It is the data which describes the properties or characteristics of the user data and its context. What is database :-Database is the collection of data in one or more data file. DBMS :-Database management system is the software which is used to create or manage the database and provides the controlled access to the database. Database from Oracle point of View:- Database is the collection of data in one or more data file. It is the collection of Logical structure and Physical Structure which are configured to maintain the