nitin singh/aao rti allahabad 1 sql nitin singh/aao rti allahabad 2 objectives §what is sql?...


5

DDL

Create TableAlter TableDrop TableCreate IndexAlter IndexDrop Index


6

DML

Insert UpdateDelete


7

DQL

Select Statement: Used to select rows from a table

Select contains following main keywords– SELECT

– FROM

– WHERE

– GROUP BY

– ORDER BY


8

Transactional Control Command

CommitRollbackSavepoint


9

DCLAlter PasswordGrantRevokeCreate Synonym


10

Data Manipulation Language

Inserting into the table INSERT INTO emp ( name , age , doj , phone_no)

VALUES(‘Anshuman’, 21 , 12/07/1999, ‘393751’) ;

Updating Existing DataUPDATE emp

SET name = ‘Sumit’

age = 31

WHERE name = ‘Anshuman’ ;


11

Data Manipulation Language

Deleting data from table DELETE FROM emp



12

Managing TablesCreating A Table

CREATE TABLE emp

( name VARCHAR2(10) NOT NULL ,

age NUMBER(2) NOT NULL ,

doj DATE NOT NULL )

STORAGE

(INITIAL 2K

NEXT 3K) ;

Continue……….


13

Managing Tables

Modifying the tableALTER TABLE emp

MODIFY (name VARCHAR2(12) NOT NULL)

ADD phone_no VARCHAR2(10) ;

Dropping the table DROP TABLE emp CASCADE


14

DQL

Selecting all the rows of table emp– SELECT *

FROM emp

Selecting phone no. & age of employee Anshuman from table emp

– SELECT phone_no , age

FROM emp



15

AGGREGATE FUNCTIONS

Used to provide summarization information for a SQL statement, such as COUNT,TOTAL,AVERAGE .

Aggregate functions to be covered are– COUNT

– SUM

– MAX

– MIN

– AVG


16

AGGREGATE FUNCTIONSCOUNT

– Used to return no. of rows .

– Return a numeric value when used with a query.

– Can be used with three options: */DISTINCT/ALL.

– COUNT(*) counts all the rows of a table including duplicates, whether a NULL value is contained in a column or not.

– COUNT(ALL) counts all the rows including the duplicates but excluding the rows containing NULL values.

– COUNT(DISTINCT)counts all the rows excluding the duplicate rows and the rows containing NULL values.


17

AGGREGATE FUNCTIONS

Usage:– SELECT COUNT(*)

FROM emp ;

– SELECT COUNT(DISTINCT name)

FROM emp ;

– SELECT COUNT(ALL name)

FROM emp ;


18

AGGREGATE FUNCTIONS

SUM– Used to return a total on the values of a column

– DISTINCT can be used with SUM where only distinct column values are to be added.

Usage:– SELECT SUM (age)

FROM emp ;

– SELECT SUM(DISTINCT age)

FROM emp ;


19

AGGREGATE FUNCTIONS

AVG– Used to find the averages for a group of rows.

– Can be used with DISTINCT command when average of distinct rows is to be found out.

Usage:– SELECT AVG(age)

FROM emp ;

– SELECT AVG(DISTINCT age)

FROM emp ;


20

AGGREGATE FUNCTIONS

MAX– Used to return the maximum value of a column in a group

of rows.

– NULL values are ignored .

Usage:– SELECT MAX(age)

FROM emp ;


21

AGGREGATE FUNCTIONS

MIN– Used to return the minimum value of a column for a group

of rows.

– NULL values are ignored .

Usage:– SELECT MIN(age)

FROM emp ;


22

ACCESSING DATA FROM MULTIPLE TABLES

By joining the tablesBy using nested queries.By using compound queries


23

JOIN

Join combines two or more tables in order to retrieve data from multiple tables.

ExampleSELECT name , address

FROM student , stu

where student.stid = stu.stid ;


24

Sub Query

Query within another querySub query is used to return data that will be

used in the main query as a condition to furthur restrict the data to be retrieved .

Used with Select , Insert , Update , Delete statements.


25

COMPOUND QUERY

Includes two or more SELECT statementsFormed by using

UNION,INTERSECT,EXCEPT operators.


26

INDEX

Pointer to the database. When index is created , it records the location of values in a

table that are associated with the column that is indexed. Entries are added to the index when new data is added to the

table . When a query is executed against the database and a condition

is specified on a column in the WHERE clause that is indexed, the index is first searched for the values specified in the WHERE clause . If the value is found in index , the index

returns the exact location of the searched data in the table.


27

INDEXTypes of index

– Single column index

– Unique index

– Composite index Single Column Index

– Based on only one table column

Creating Single Column Index– CREATE INDEX name_idx

ON emp(name) ;


28

INDEX

Unique Index– Does not allow any duplicate values to be inserted into the

table

Creating Unique IndexCREATE UNIQUE INDEX name1_idx

ON emp(name) ;


29

INDEX

Composite Index– An index on two or more columns

Creating Composite IndexCREATE INDEX nam1_idx

ON emp(name, age) ;


30

INDEX

Dropping the indexDROP INDEX name_idx ;


31

INDEX

Conditions where index should be avoided– Should not be used for small tables.

– Should not be used on the columns that contain high no. of null values.

– Columns that are frequently manipulated should not be indexed .

Conditions where index should be considered– Columns that are frequently referenced in the ORDER BY &

GROUP BY clauses should be considered for indexes.

– Indexes should be created on the columns with high no. of unique values.

– Foreign keys are excellent candidates for index , as they are often used to join parent table.


32

VIEWA virtual table.Looks like a table and acts like a table.Does not require physical storage space. ORDER BY clause can’t be used in

CREATE VIEW but GROUP BY clause can be used which has same effect as ORDER BY clause


33

VIEW

Creating a view– CREATE VIEW nam_vew AS

SELECT emp.name ,emp.age , detail.address , detail.status

FROM emp , detail

WITH CHECK OPTION ;

Dropping a view– DROP VIEW nam_vew ;


34

SYNONYM

Another name for table or viewUsually created so that a user can avoid

having to qualify another user’s table or view to access the table or view.

Creating a synonym– CREATE SYNONYM employ FOR emp ;

Dropping a synonym– DROP SYNONYM employ ;


35

Managing Database Transactions

Transaction: Sequence of work accomplished in a logical manner.

Commands to control transactions:– COMMIT

– ROLLBACK

– SAVEPOINT


36

Managing Database Transactions

Commit• Used to save changes invoked by a transaction to

the database.

• Syntax: COMMIT[WORK] ;

Rollback• Used to undo transactions that have not already been

saved to the database.

• Syntax: ROLLBACK[WORK] ;


37

Managing Database TransactionsSavepoint

• It is a point in a transaction that one can roll the transaction back to without rolling back the entire transaction.

• Syntax: SAVEPOINT s1 ;

ExampleSAVEPOINT s1 ;

DELETE FROM emp


SAVEPOINT s2 ;

DELETE FROM emp

WHERE name = ‘Sumit’ ;

SAVEPOINT s3 ;

ROLLBACK s2;

nitin singh/aao rti allahabad 1 sql nitin singh/aao rti allahabad 2 objectives §what is sql?...

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