Structured Query Language (SQL) is a language that provides
an interface to relational database systems.
In common usage SQL also encompasses DML (Data Manipulation
Language), for INSERTs, UPDATEs, DELETEs and DDL (Data
Definition Language), used for creating and modifying
tables and other database structures.
sql is a universally accepeted query language whic acts an
interface to the relational databases to fetch,insert and
manipulate the data existing in the database.
sql encompasses of five parts
1.Data Retrieval Language:the commands used to select data
from the database.this includes
2.Data manipulation Language:commands to manipulate the
data existing in the database.commands in this are
3.Data Definition Language:commands to define and create
the database ojects like tables ,views etc.commands in this
4.Tranaction control Language:the commands in this are
5.Data Control Language:the commands in this are
SQL IS A STRUCTURED QUERY LANGUAGE THROUGH WHICH WE CAN
COMMUNICATE WITH THE ORACLE SERVER AND SQL STATEMENTS ARE
DIVIDED INTO FIVE STATEMENTS i:e. Data defintion language
(DDL) which is used in creating the tables,views. In DDL
where as Data Manipulation Language(DML)command is used to
manipulate the data.In DML
the third one is Data retrieval i:e. the select command
the fourth one is Transcation control i:e.
the fifth one is data control language(DCL) i:e.
create table Student (id number(4) primary key, Name
It creates the table Student which has two fields id i.e.
Student id and Name i.e. the student name. The number and
varchar2 are the data types of id and Name respectively.
Field 'id' has the size 4 means it can take id up to 4
digits and same for Name, it can take the size up to 20
characters. And also added the constraint Primary key to the
This command is used to add, drop columns in a table. The
syntax for this command is
alter table tablename add colname1 datatype [constraint];
alter table tablename drop column colname1;
alter table Student add DOB date;
This command is used to add new field DOB in Student table.
It's datatype is date. This is also used for drop column
from the table. It will drop the DOB field by query given below-
Alter table Student drop column DOB;
The syntax for this command is-
drop table tablename;
drop table Student;
This statement is used for destroy the table from database.
Data definition language.
Mainly 3 commands are available here,create,Drop,Alter.
•Data manipulating language
•This wil mainly contains select,insert,delete,update operations
DETAILED SYTAX AND EXAMPLES:-
CREATE: SQL CREATE is the command used to create data objects, including everything from new databases and tables to views and stored procedures. In this lesson, we will be taking a closer look at how table creation is executed in the SQL world and offer some examples of the different types of data a SQL table can hold, such as dates, number values, and texts.
CREATE [TEMPORARY] TABLE [table name] ( [column definitions] ) [table parameters]
Ex: CREATE TABLE employees (
id INTEGER PRIMARY KEY,
first name VARCHAR(50) NULL,
last_name VARCHAR(75) NOT NULL,
dateofbirth DATE NULL
DROP: - To destroy an existing database, table, index, or view
Drop table tablename;
Ex: DROP TABLE employees;
ALTER: SQL ALTER is the command used to add, edit, and modify data objects like tables, databases, and views. ALTER is the command responsible for making table column adjustments or renaming table columns. New table columns can also be added and dropped from existing SQL tables.
SELECT; SQL SELECT may be the most commonly used command by SQL programmers. It is used to extract data from databases and to present data in a user-friendly table called the result set.
•Select table tupile tablename
Ex: select customername from employe;
INSERT: To use the INSERT command, we must first have an understanding of where we would like to insert data and what types of data we want to insert. Do we plan on inserting numbers? Strings? Files? Let's return to the orders table we created in an earlier lesson.
•Insert into tablename(attributename) values(corresponding values that we are like to give)
Ex: Insert into employe (custname) value(“vijitha”);
DELETE: In the SQL world, databases, rows, and columns all have one thing in common: once a DELETE statement has been executed successfully against them, the data they once contained is lost forever! Be very careful with these commands and be sure to properly backup all data before proceeding with any type of DELETE command(s).
Delete from tablename where[include the condition];
Ex: Delete from employe where custname=vijitha;
UPDATE: SQL UPDATE is the command used to update existing table rows with new data values. UPDATE is a very powerful command in the SQL world. It has the ability to update every single row in a database with the execution of only a single query. Due to UPDATE's supreme authority, it is in your best interest to always include a WHERE clause when working with UPDATE query statements. That way, you will not accidentally update more rows than you intend to.
Udate tablename set any condition where any condition;
Ex: update orders set custname=’amith’ where age=’20’;