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SQL (Structured Query Language) 

Presented by: Manohar PrasadSpecialization: IB+ITRoll No.- 1999/01030003

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Structured Query Language (SQL)

SQL allows user to access data in relationaldatabase management systems, such as Oracle,

 Access, SQL Server, FoxPro, Informix and others,by allowing users to describe the data the userwishes to see.

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SQL statements are issued for thepurpose of:

Data definition - Defining tables and structures

in the database .

Data manipulation - Inserting new data,

Updating existing data, Deleting existing data, and

Querying the Database ( Retrieving existing datafrom the database).

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DDL Statements

CREATE  - Create new database objects such as tables orviews

DROP    - Drop a database object such as a table, viewor index

ALTER  - Change an existing table, view or index definition

GRANT   - Allow another user to access database objects

such as tables or views (For Data Control )

REVOKE  - Disallow a user access to database objects such astables and views (For Data Control ) 

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DML Statements

SELECT   - Retrieve data from a database table

INSERT   - Insert new data into a database table

UPDATE    - Change the values of some data items in adatabase table

DELETE    - Delete rows from a database table

TRUNCATE - Delete all rows from a database table (can notbe rolled back)

COMMIT - Make all recent changes permanent (DML -transactional)

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Creating Tables

Tables are defined with the CREATE TABLE command. This command creates an empty table,

a table with no rows. Basically defines a table name as describing a

set of named columns.

Defines the data types and sizes of thecolumns.

Each table must have at least one column.

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Type description  Oracle SQL 

variable-length char. string VARCHAR2(l)

fixed-length char. string CHAR(l)number NUMBER 

date DATE

The main SQL data types

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  Creating a table

E.g.:- 1) CREATE TABLE Employee (Emp_No Char(4),

Name Varchar2(15),

 Address Varchar2(15),

DOB Date,

Salary Number(9,2) );

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Creating table with constrains

e.g.:- 2) CREATE TABLE Employee (

Emp_No Char(4) Primary Key,

Name Varchar2(15) Not Null,

 Address Varchar2(15),

DOB Date,

Salary Number(9,2) Check (Salary > 3500) );

Primary Key

 Always Salarymust be > 3500Name field

Cannot be null

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Altering a Table

Once created, tables can be altered to accommodatechanging needs.

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Eg:- 1) ALTER TABLE Employee

ADD Sex char(1);

+

 Add new column to the table

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2) ALTER TABLE Employee

DROP COLUMN Sex ; 

Delete a existing column from the table

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  Displaying Table Structure 

E.g.:- DESCRIBE Employee; 

Name Null? Type

--------------- -------------- -------------

EMP_NO NOT NULL CHAR(4)

NAME VARCHAR2(15)

 ADDRESS VARCHAR2(15)

DOB DATE

SALARY NUMBER(9,2)

SEX CHAR(1)

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Entering Values to a table

SQL provides the key word INSERT to add data to a table.

E.g.:- 1) INSERT INTO Employee

 VALUES (‘E001’,’Ranjith’,’Matara’,’12-Feb-76’,7400); 

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Entering Values to a table

Naming columns for insert

2) INSERT INTO Employee (Emp_No, Name, Salary)VALUES (‘E001’,’Ranjith’,7400.00); 

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