Download Structured Query Language - CBSE Plus Two Help Files

It is a database programming language
developed by IBM in the early 1970’s.
It is used for managing and retrieving data stored
in database system
Mostly all DMMS ‘s support SQL
SQL can execute queries against a database
SQL can retrieve data from a database
SQL can insert records in a database
SQL can update records in a database
SQL can delete records from a database
SQL can create new database
SQL can create tables in a database
SQL can create views in a database
SQL can set permissions on tables , procedures and
tables
SQL commands consists of English language words
such as create, insert , delete etc, so it is easy to
learn
SQL is a non procedural language. We simply
specify what information is to be retrieved rather
than how to retrieve it
SQL is a keyword based language . Each command
of SQL begins with a unique keyword
SQL is a free format language , ie parts of SQL
statements do not have to be typed at particular
locations on the screen
SQL is a portable language . If we follows standard
syntax we can move SQL commands from one
DBMS to another
SQL can be used by variety of users from
DBA(Database Administrators) , application
developers to end users.
1. Data Definition Language (DDL) :
CREATE,ALTER,RENAME, DROP
2. Data retrieval : SELECT
3. Data Manipulation Language (DML) :
UPDATE,DELETE,INSERT
4. Transaction Control Language (TCL) :
COMMIT,ROLLBACK,SAVEPOINT
5. Data Control Language
: GRANT,REVOKE
DDL commands are subset of SQL commands .These
commands are used to perform three main function
on database objects.(tables).They are
1. Defining or creating database objects through
CREATE statement
2. Modifying database objects through ALTER
statement
Removing definition of database object through
DROP statement
Definition of all database objects is stored in
permanent table called data dictionary.
Data dictionary stores data about data called metadata
Subset of SQL commands used to query and
manipulate the database.
INSERT : Inserting new records in to a table or
relation.
UPDATE : Modifying existing records.
DELETE : Deleting unwanted records.
SELECT statement can be considered in the
category of DML.
It is used to retrieve existing records from the
database
1. Procedural DML : It not only require a user to
specify what data is needed, but also the
procedure of how to retrieve the data.
2. Non-Procedural DML : It require only to specify
what data is needed without giving details of
procedure.
Eg : INSERT,UPDATE,DELETE,SELECT
When we make changes on a table suing
insert,delete or update,these are temporary
changes.
COMMIT is used to make theses changes
permanent. After applying COMMIT
transaction is successfully completed.
It is managed by TCL commands
COMMIT : used to make the changes permanent
ROLLBACK : used to undo all changes of a
transaction
SAVEPOINT : Identify a point or mark in a
transaction since COMMIT.
Incase of failure u can undo last transaction , ie
rollback up to that save point
It controls type of data access to the database
GRANT : is used to assign user’s access
privileges to the database.
REVOKE : used to withdraw the access
privileges given by GRANT
1. SQL commands can be typed in lower or
uppercase . It is not case sensitive
2. It can be typed in a single line or more than one
line
3. A semi colon is used to terminate SQL
command.
4. A comma (,) can be used to separate parameter
5. Characters and date constraints or literals must
be enclosed in single quotes (‘A’)
Reserved words can’t be used as identifier’s name .
Some of the words are
ADD,SET,DATE,CHAR,DROP,ELSE,INTO,LIKE
,CREATE,DELETE,VARCHAR,AS,OR,ON,FL
OAT,ALTER,CHECK etc
A command can be typed either in full or first four
characters
1. Relation or table : used to ……………..
2. View : it is a logical table , part of original table .
Different views of database are assigned to
different users.
3. Sequence : it is used to identify the records in a
table by generating the primary key value to them
4. Index : it improve response time of queries
5. Synonym : Used to give alias name or alternative
names to objects
1. Name must be 1 to 30 characters long. Name of
the database can be 8 characters long
2. Names of objects are not case sensitive
3. Names should not contain quotation marks
4. First character of the name must be an alphabet.
5. Names of alphabets can have alphanumeric
values
6. Reserved words cannot be used for naming
objects
1. NUMBER
It may contain a number with or without
decimal point and a sign. An attribute of a relation
can have numbers in three forms
a). NUMBER : Here we don’t specify the width or
precision . Default one ‘ll be taken
b). NUMBER (P) : Here we specify the width or
precision without any decimal point.
It is mainly used for EmpNo, Age
c). NUMBER (P,S) : Here we specifies both
precision P and scale S .
P is total number of decimal digits and
Scale S is total number of digits to the right of the
decimal point.
2. CHARACTER
It contain fixed length character
data . Abbreviated as CHAR , specified as
CHARACTER [(Size)] or CHAR [(Size)].
It is used for Item_code , the length of which
remains same for all items
3). VARCHAR2
It contain varying length character
data and is specified as
VARCHAR2 (Size)
Maximum size must be given .Attributes such as
EName , DName uses this data type in which
length varies frequently.
4). DATE
Used to store date and time value . It is
defined simply as
DATE
It is stored in standard format as
DD- MON-RR
DD : Day
MON : Month
RR : Year
Points to remember :
1. Every SQL command must be terminated
with a semicolon (;)
2. SQL is a case insensitive language
Presentation style
1. All SQL key words are written in capital
letters
2. Table names are written with their first letter
capital
3. All SQL commands are indented properly to
provide readability
1. CREATE TABLE :
Each table in the database
is created by using CREATE TABLE
command
Syntax :
CREATE TABLE <table name>
(<column name> <data type> [size],
< column name> <data type> [size]…..);
Table name and column name are given by the user.
When a table is created it must have at least one
column.
Table is empty , it has no data. Only the definition
of the table is stored in the database.
This definition is called schema of the table
Eg :::@@ IMP @@:::
1. Create a table EMPLOYEE which has the
following columns
Column Name
Data Type
Description of column
EmpNo
Ename
Hire_date
Job
Salary
DeptNo
Number (3)
Varchar2(30)
Date
Varchar2(15)
Number (7,2)
Number (2)
Employee Identity Number
Employee Name
Date of joining of Employee
Job title of employee
Basic salary of employee
Department number of employee
CREATE table EMPLOYEE (EmpNo Number (3),
EName Varchar2(30) , Hire_date Date , Job
Varchar2(15) , Salary Number (7,2) , DeptNo
Number (2)) ;
Table created
Constraints :
Constraints are the mean by which you can
prevent invalid data entry in to the table.
Eg : salary must not exceed 30,000.00
Constraints are stored in data dictionary . if we don’t
specify the name of the constraint Oracle
automatically gives a name. (SYS_Cn)
We can view constraint in User_constraint in data
dictionary,
Various constraints which can be defined on
database object are
1.
2.
3.
4.
5.
6.
NOT NULL
UNIQUE KEY
PRIMARY KEY
FOREIGN KEY
CHECK
DEFAULT
You can create constraint either
1. At the time when the table is created using
CREATE TABLE or
2. After the table has been created using ALTER
TABLE.
constraint can be defined at two levels when table
is created
Column level : It is used when it is to be applied
on a single column
Table level : It is used when it is to be applied on
more than one column.
All the constraints except NOT NULL can be
defined at table level
Detail about different types of constraints
Null ???
It is a value which is unknown ,unavailable ,
unassigned or inapplicable.
It is neither a zero or a blank space, because zero
is a numeric value and space is a character.
Column of any data type can contain NULLS
NOT NULL ensures that the column cannot
contain a null value.
SQL >
Create Table Student
( Name Varchar2 (25) Not Null ,
Class Number (2) ) ;
Explain !!!
Here constraint name is unnamed. We can provide
name by the command
Create Table Student
( Name Varchar2 (25) constraint Name_st Not Null ,
Class Number (2) ) ;
Here Name_st is the constraint name given by us
It specifies a column or combination of columns
whose value must be unique for all rows in the
table.
No two rows can have duplicate values.
It can be defined at the column level or table
level.
Column level : It references a single column
SQL >
Create Table Student
(Rollno Number (3) Unique,
Name Varchar2(25) Not Null,
Class Number (2)
);
Here no two records can have same roll number
Table level :
It references one or more columns
SQL >
Create Table Student
(Rollno Number (3),
Name Varchar2(25) Not Null,
Class Number (2),
Unique (Rollno)
);
Column included in unique constraint is known as
UNIQUE KEY
One limitation of candidate key is that it allows
null values in the column.
Primary key constraint allow two things
Unique identification of each row in the table
No column that is a part of primary key can
contain a null value
It can be defined at column or table level
Column level :
SQL >
Create Table Student
(Rollno Number (3) PRIMARY KEY,
Name Varchar2(25) ,
Class Number (2)
);
Null value and duplicate for Rollno is not allowed
Table level :
SQL >
Create Table Student
(Rollno Number (3),
Name Varchar2(25) ,
Class Number (2)
PRIMARY KEY (Name , Class) ) ;
It designates a column or combination of columns
as a foreign key and establishes it’s relationship
with a primary key or unique key in different
table.
Eg : EMPLOYEE and DEPARTMENT
Column level :
SQL >
CREATE TABLE Employee
(EmpNo Number (3),
………………….
salary Number (7,2),
DeptNo Number(2) REFERENCES
Department (DeptNo) ) ;
Table level :
SQL > CREATE TABLE Employee
(EmpNo Number (3),
………………….
salary Number (7,2),
DeptNo Number(2)
FOREIGN KEY (DeptNo) REFERENCES
Department (DeptNo) ) ;
Values in some of the columns are to be within a
certain range or they must satisfy certain
condition.
Given to column so that all value must satisfy the
condition.
SQL > CREATE TABLE Employee
(EmpNo Number (3),
Ename Varvhar2(30),
Salary Number (8 , 2) CHECK (salary > 0) ,
…………………… );
We can apply it for table level also
It is used to assign a default value to a column.
It prevents null entry in a row.
SQL >
Create Table Student
(Rollno Number (3) UNIQUE,
Name
Varchar2(25) NOT NULL,
Class
Number (2)
Adm_date DATE DEAFULT SYSDATE );
Syntax :
ALTER TABLE Tablename ADD
[constraint type] (col) ;
Eg : ALTER TABLE Employee ADD PRIMARY
KEY (EmpNo) ;
Syntax :
ALTER TABLE Tablename
DROP CONSTRAINT Constraint name ;
Eg : ALTER TABLE Employee
DROP PRIMARY KEY ;
OR
ALTER TABLE Employee
DROP CONSTRAINT EmpName ;
Syntax :
ALTER TABLE Tablename DISABLE
CONSTRAINT constraint_name ;
Eg : ALTER TABLE Employee
DISABLE CONSTRAINT EmpNumber ;
Syntax same as that of previous one
Eg:
ALTER TABLE Employee
ENABLE CONSTRAINT EmpNumber ;
E g : SELECT constraint_name , column_name
from user_cons_columns
where tablename = ‘Employee’;
Dropping a table not only deletes the data contained
in the table but also removes the definition of it’s
structure from the database.
Syntax : DROP TABLE <Table name> ;
E g: To drop employee table
DROP TABLE Employee ;
The structure of a table can be altered by applying
the alter table statement.
Table can be altered in one of the three ways
1. By adding a column to an existing table
2. By changing a column definition (data type)
3. By dropping a column of a table.
Adding a new column in a table
Syntax : ALTER TABLE <table name>
ADD <column name> <data type>
[constraint definition] ;
E g : ALTER TABLE Student
ADD grade char(1);
SQL > ALTER TABLE Student
ADD Percentage Number (3)
CHECK (Percentage < =100) ;
Modifying existing column
It changes the data type or size of an existing
column. Here we uses MODIFY clause.
Syntax : ALTER TABLE <table name>
MODIFY (<column name> <data type>
[size]) ;
Here
1. Width of the column can be increased at any time.
2. Number of decimal place in a NUMBER column
can be increased or decreased at any time
3. Data type of a column can only be changed if the
column contains null values
Eg : NUMBER (7 , 2) to NUMBER (8 , 2)
ALTER TABLE Employee
MODIFY (Salary Number (8,2));
A column can be dropped from a table if it is no
longer required.
Syntax :
ALTER TABLE <Table name>
DROP COLUMN <column name> ;
We can drop more than one columns at a time
ALTER TABLE <Table name>
DROP COLUMN (<column 1> , <column 2>) ;
To drop grade from student table sql command is
SQL >
ALTER TABLE Student
DROP COLUMN grade ;
It will drop the column’s definition from the
database
We can change the name of an existing table by
using RENAME command.
Syntax :
RENAME <table name> to
<new table name>
Eg: RENAME Employee To Empl ;
TRUNCATE command deletes all the rows of a
table. It empties a table completely
Syntax : TRUNCATE TABLE <Table name> ;
E g: TRUNCATE TABLE Employee ;
Syntax for adding a comment to a column of a table
is
COMMENT ON COLUMN <table name> .
<column name > IS ‘COMMENT’;
Eg : COMMENT ON COLUMN Employee.Job
IS ‘Job Title Of Employee’;
Comment on table
COMMENT ON TABLE Employee IS ‘Details of
Employee’;
Syntax : COMMENT ON COLUMN <Table name>
. <Column name > IS ‘ ’ ;
Eg:
COMMENT ON TABLE Employee IS ‘ ’;
COMMENT ON COLUMN Employee.Job IS ‘’;
These are used to manipulate the existing object of
a database such as tables.
1. INSERT statement
It is used to store data in a table.
Syntax :
INSERT INTO <table name>[<column list>]
VALUES (<list of values>) ;
SQL >
INSERT INTO Employee Values
(111,’Lucky’,’10-June-2003’,’Clerk’) ;
We can view the table by
SQL > SELECT * from Employee ;
When we do not want to supply values for all the
columns we ‘ll use it.
INSERT INTO Employee
(Empno,Ename,Hire_date , salary) Values
(112,’Mansi’,’05-Sep-2011’,1300) ;
INSERT INTO Employee values
(112,’Mansi’, ’05-Sep-2011’,NULL ,1300,Null);
SQL > INSERT INTO Employee values
(&Empno , &Empname , &Job , &salary);
We can insert the rows from another table by
INSERT command.
Here we insert values in Employee1 from
Employee table
SQL >
INSERT INTO Employee1
Select * from Employee
where Empno BETWEEN 103 and 105 ;
It changes or modifies the value of specified
column in a table.
Syntax :
UPDATE <table name>
SET <column name >=<value>
where <condition>;
UPDATE Employee1
SET Salary = Salary + 1500 , Job = ‘Manager’
where Deptno IN (11,12,13) ;
UPDATE Employee SET job = NULL ;
UPDATE Employee1
SET job = ‘Manager ‘
WHERE Empno = (Select EmpNo From
Employee where Hire_Date = ’05-Nov-1999’ ) ;
It does exactly opposite to that of an INSERT
statement.
It is used to DELETE rows from a table
Syntax :
DELETE [FROM] <table name>
[WHERE <condition>];
Where clause is used to restrict the number of rows
to be deleted
DELETE with WHERE clause
Syntax :
DELETE [FROM] <table name>
WHERE <condition> ;
SQL >
DELETE from Employee
where Salary < 25000 ;
DELETE without WHERE clause
Syntax :
DELETE FROM <table name> ;
SQL >
DELETE FROM Employee1 ;
OR
DELETE * FROM Employee1 ;
Deleting rows based on conditions
from another table
SQL >
DELETE FROM Deptt
WHERE DeptNo Not In
(Select DeptNo from teacher) ;
A transaction is a unit of work that contains
logically related statements . A transaction has a
beginning and an end.
Commit and rollback statements are used to
control transaction.
Commit is used to finish the current transaction by
making the changes permanent.
After applying the commit we cannot retain the
previous state of the data.
SQL >
SQL >
UPDATE Teacher
Set Salary = 18000
Where Tno = 103;
COMMIT;
ROLLBACK is used to cancel or undo all the
changes in the current transaction.
SQL >UPDATE Teacher Set Salary = 18000
WHERE Tno=103 ;
SQL >ROLLBACK ;
SQL > Select * from teacher ;
It is used to retrieve information from a table . it
can be used to access a row , a column , a group
of rows , a group of columns or all the rows and
columns in a table.
Syntax :
SELECT <column1>,[<column2>…]
FROM <table name> ;
EMPNO
ENAME
HIRE_DATE
JOB
SALARY
DEPTNO
101
Sunil
01-Jul-01
President
27000
11
102
Pavitra
11-Jan-02
Clerk
18000
12
103
Seema
18-Feb-95
Manager
20000
13
104
Sanjay
28-Aug-97
President
23000
14
105
Deepa
05-Nov-99
Operator
13000
11
106
Sanker
09-Mar2006
Manager
22000
11
107
Surekha
29-Apr-03
President
25000
13
Selecting all columns
Syntax :
SELECT * FROM <table name> ;
• is used for displaying all the columns from a
table.
To retrieve all columns from Employee
SQL > SELECT * FROM Employee ;
SELECT <column1>, <column2>,….
FROM <table name> ;
Display Empno , Ename and job from Employee
Syntax :
SQL > SELECT Empno , Ename , Job
FROM Employee ;
Powerful feature of SQL is pattern matching using
LIKE .
Two symbols are used to construct the search string
1.
%
Represent any sequence of zero or
more characters
2. _
(underscore)
Represent any single
character
To list all the employees whose names begin with
letter ‘S’ in Employee table.
SQL >
SELECT * FROM Employee
WHERE Ename LIKE ‘S%’ ;
To list the details of employee having the second
character of their name as ‘a ‘ in the table
Employee
SQL >
SELECT * FROM Employee
WHERE Ename LIKE ‘_a%’ ;
Display name job and department number of
employees whose name if of seven characters long
from Employee table
SQL >
SELECT Ename , Job , DeptNo
FROM Employee
WHERE Ename LIKE ‘_ _ _ _ _ _ _ ’;
It is for testing null values in a table
To list class and name of students who have not
been assigned any grade .
SQL >
SELECT Name , Class FEOM SPORTS
WHERE Grade IS NULL ;
1. OR
List the rollno , name , game ,grade of all students
with game either cricket or tennis
SQL >
SELECT rollno , name , game , grade from
SPORTS
WHERE game = ‘Tennis’ OR game =
‘Cricket’ ;
2. AND
List the name game grade of all the students in table
SPORTS with game = tennis and grade = A is
SQL > SELECT name , game , grade from SPORTS
WHERE game= ‘tennis’ AND grade =‘A’;
3. NOT
List the details of all the students not in class 7 ,8,10
SQL >
SELECT * FROM SPORTS
WHERE class NOT IN (7,8,10) ;