CBSE Class 12 Computer Science Database And SQL Concepts

Data :- Raw facts and figures which are useful to an organization. We cannot take decisions on the basis of data.

Information:-Well processed data is called information. We can take decisions on the basis of information

Field: Set of characters that represents specific data element.

Record: Collection of fields is called a record. A record can have fields of different data types.

File: Collection of similar types of records is called a file.

Table: Collection of rows and columns that contains useful data/information is called a table. A table generally refers to the passive entity which is kept in secondarystorage device.

Relation: Relation (collection of rows and columns) generally refers to an active entity on which we can perform various operations.

Database: Collection of logically related data along with its description is termed as database.

Tuple: A row in a relation is called a tuple.

Attribute: A column in a relation is called an attribute. It is also termed as field or data item.

Degree: Number of attributes in a relation is called degree of a relation.

Cardinality: Number of tuples in a relation is called cardinality of a relation.

Primary Key: Primary key is a key that can uniquely identifies the records/tuples in a relation. This key can never be duplicated and NULL.

Foreign Key: Foreign Key is a key that is defined as a primary key in some other relation. This key is used to enforce referential integrity in RDBMS.

Candidate Key: Set of all attributes which can serve as a primary key in a relation.

Alternate Key: All the candidate keys other than the primary keys of a relation are alternate keys for a relation.

DBA: Data Base Administrator is a person (manager) that is responsible for defining the data base schema, setting security features in database, ensuring proper functioning of the data bases etc. Data types of SQL Just like any other programming language, the facility of defining data of various types is available in

SQL also. Following are the most common data types of SQL.

       1) NUMBER

       2) CHAR

       3) VARCHAR / VARCHAR2

       4) DATE

       5) LONG

       6) RAW/LONG RAW

Constraints:

Constraints are the conditions that can be enforced on the attributes of a relation. The constraints come in play when ever we try to insert, delete or update a record in a relation.They are used to ensure integrity of a relation, hence named as integrity constraints.

1. NOT NULL

2. UNIQUE

3. PRIMARY KEY

4. FOREIGN KEY

5. CHECK

6. DEFAULT

i. Not Null constraint : It ensures that the column cannot contain a NULL value.

ii. Unique constraint : A candidate key is a combination of one or more columns, the value of which uniquely identifies each row of a table.

iii. Primary Key : It ensures two things : (i) Unique identification of each row in the table.

(ii)No column that is part of the Primary Key constraint can contain a NULL value.

iv. Foreign Key : The foreign key designates a column or combination of columns as a foreign key and establishes its relationship with a primary key in different table.
Create table Fee

(RollNo number(2) Foreign key (Rollno) references Student (Rollno),

Name varchar2(20) Not null, Amount

number(4), Fee_Date date);

v. Check Constraint : Sometimes we may require that values in some of the columns of our table are to be within a certain range or they must satisfy
cceorntdaiintions.

Example:

Create table Employee

(EmpNo number(4) Primary Key,

Name varchar2(20) Not Null,

Salary number(6,2) check (salary > 0),

DeptNo number(3)
);
Data Manipulation in SQL

DML Commands are as under:

SELECT - Used for making queries

INSERT - Used for adding new row or record into table

UPDATE- used for modification in existing data in a table

DELETE – used for deletion of records.

INSERT Statement

To insert a new tuple into a table is to use the insert statement

insert into <table> [(<column i, . . . , column j>)] values (<value i, . . . , value j>);

INSERT INTO student VALUES(101,'Rohan','XI',400,'Jammu');

While inserting the record it should be checked that the values passed are of same data types as the one

which is specified for that particular column.

For inserting a row interactively (from keyboard) & operator can be used.

e.g INSERT INTO student VALUES(&Roll_no’,’&Name’,’&Class’,’&Marks’,’&City’);

In the above command the values for all the columns are read from keyboard and inserted into the table student.

Please refer to attached file for CBSE Class 12 Computer Science Database And SQL Concepts