sqlbysandeep

SQL

Structured Query Language

SQL is language use for creating, accessing and manipulating database systems. SQL statements are used to retrieve and update data in a database. SQL works with database programs like MS Access, DB2, Informix, MS SQL Server, Oracle, Sybase, etc.

Database is collection of data Stored in table format.Each table is identified by a name . Tables contain records (rows) and columns.Below is an example of a table called “employee":

Id Name Sal

1 Aditya 25000

2 Vaidehi 17000

For Performing Operations on the data stored in tables different commands are available in sql. SQL commands are categorized in different groups

DDL : Data Definition LanguageDML: Data Manipulation Language TCL : Transaction Control Language

DATA DEFINITION LANGUAGE(DDL)

DDL include three commands

•CREATE - Creates a new database table or object.• ALTER - Alters (changes) a database table or Object We can Add ,Modify and Drop column• DROP - Deletes a database table or Object

CreateSyntax:Create table table_name( column1 datatype(size), column2 datatype(size), . . columnn datatype(size));

Example:Create table Employee(id number(3), name varchar2(10), salary number(10));

EFFECT OF CREATE COMMANDId Name salary

AlterSyntax: Alter table table_name ADD/MODIFY/DROP (column specification);

Example Alter table employee Add (Address varchar2(10)); Alter table employee modify(Address varchar2(12)); Alter table employee Drop(Adress );

EFFECT OF ALTER COMMANDID NAME SALARY

Alter table employee Add (Address varchar2(10));

ID NAME SALARY ADDRESS

Alter table employee Drop(Address );

ID NAME SALARY

DropSyntax:Drop table table_name;

Example: Drop table employee;

DATA MANIPULATION LANGUAGE (DML)

Data Manipulation Language (DML) include select,update,delete,insert:

•SELECT - Use for retrieving data from a database table •UPDATE – Use for updating data in a database table •DELETE – Use for deletes data from a database table •INSERT - Use for inserts new data into a database table

Syntax

Select * or column1,column2..column n from table_name[where condition];

ExampleSelect * from employee;

Select name from employee;

SELECT STATMENT

INSERT STATMENTSyntax

INSERT INTO table_name[(column1,column2,…)]

VALUES (value1, value2,....) ;

Example;

Insert into emp(id,name,salary)values(101,’Aditya’,100000);

Id Name Sal

1 Aditya 100000

2 Vaidehi 17000

UPDATE STATMENTSyntax

UPDATE table_name

SET column_name = new_value

WHERE column_name = some_value;

Example:

update emp

set salary=50000

where id=101;

Id Name Sal

101 Aditya 50000

102 Vaidehi 17000

DELETE STATMENT

Syntax

DELETE FROM table_name

[WHERE column_name = some_value ]

Example:

delete from employee

where id=101;

Id Name Sal

102 Vaidehi 17000

Thank you!