11th Class RDBMS information

1. Concept of  a data:
 --  A Database System is basically a record keeping system.
 –   Collected form of data is known as database.
 – “Database is actually a collection of interrelated data so that it can be used by various applications.

2. Relation:
A table is a combination of rows and columns which is also known as Relation.
Relation :  Basically a relation is a table. Its a collection of data in rows and columns

3.Attributes:
 columns of a table are known as attributes

4. Tuples:
 rows of a table are known as tuples

5. Candidate key
 Its a group of attributes which have the properties to be selected as a primary key i.e. These attributes shows their candidature to be a Primary Key.

6. Primary key
It is a group of one or more attributes which are used to uniquely identify records of a relation and can be used to establish relationship with other relation.  Generally all master tables have primary keys. For ex- RollNo in Student table.

7.  Alternate key

 A candidate key which is not a primary key is known as  alternate key.

8. Degree of the table
   In a relation, number of attributes or columns is known as its Degree.

9. Cardinality of  the table
 In a relation, number of tuples or rows is known as its Cardinality.

10. Foreign key
In a table, a non-key attribute which is derived from primary key of some other table is known as foreign key in present table.


DDL and DML Commands:
DDL
-- Command under this category are used to create or modify scheme of database.  It is used to create data dictionary.
– Data Dictionary is a kind of metadata means Data about Data.

 A standard DDL  should have following functions
 – It should identify the types of data division.
 – It should give a unique name of each data item.
 – It should specify the proper data type.
 – It may define the length of data items.
 – It may define the range of values of Data items.

Following commands are under this category-
 – Create, alter and drop schema Objects • Create table,  create database, 
• Alter Table  • Drop Table 

DML
– Data manipulation means- 
 • Accessing the stored data from a Database.
 • Insertion of new information into the Database.
 • Deletion of information from the Database.
 • modification of information in the Database.