sqljoinsviewsindexes-110110013829-phpapp01

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JOINS VIEWS INDEXES

What Is The Difference Between SQL and PL/SQL?

There are so many variants of SQL that it is hard sometimes to figure out what to use !ere

is a short arti"#e that $rief#y e%ains the differen"e $etween SQL and 'L(SQL En)oy*

What is SQL?

SQL +&ronoun"ed ,se-ua#./ stands for Stru"tured Query Language Withe SQL0 you "an view

data 1 "a##ed Data Definiton Language or DDL and mani&u#ate data 1 "a##ed Data

2ani&u#ation Languate or D2L 3## of the a$ove are )ust a fan"y way to say that with SQL0the user "an $oth view and a#ter re"ords in the data$ase To he#& 0 here are a "oue of

-ueries4

What is PL/SQL?

The offi"ia# answer is from the 'L(SQL 5ser 6uide4'L(SQL0 Ora"#e7s &ro"edura# e%tension of SQL0 is an advan"ed fourth8generation&rogramming #anguage +96L/ It offers software8engineering features su"h as data

en"a&su#ation0 over#oading0 "o##e"tion ty&es0 e%"e&tions0 and information hiding 'L(SQLa#so su&&orts ra&id &rototy&ing and deve#o&ment through tight integration with SQL and the

Ora"#e data$ase!uh: That is what I thought at the $eginning ;ut at a high #eve#0 a## this means is that it

"an do a## of the things that regu#ar SQL "an do0 $ut a#so0 it is &ro"edura# and "an $e used#i>0 Java0 et"/ ?or instan"e0 you "an use #oo&s and If

Then statements in your 'L(SQL statements +'rograms/

!ere is a definition of 'L(SQL from Lewis =unningham +an Ora"#e data$ase e%&ert/4

,If I wanted to "reate my own0 very short0 definition of 'L(SQL it wou#d $e this4 'L(SQL isthe Ora"#e native &rogramming #anguage that &rovides data$ase8"entri" a&i"ation

deve#o&ment It "an native#y "a## stati" SQL and &rovides mu#tie methods of "a##ingdynami" SQL

2r =unningham a#so does a very good )o$ of s&e##ing out the differen"es $etween SQL and'L(SQL

SQL is a data oriented #anguage for se#e"ting and mani&u#ating sets of data 'L(SQL is a&ro"edura# #anguage to "reate a&i"ations @ou don7t norma##y have a ,SQL a&i"ation. @ou

norma##y have an a&i"ation that uses SQL and a re#ationa# data$ase on the $a"


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SQL JOINS

The JOIN


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The FOrdersF ta$#e4

O*Id OrderN$ P*Id

C KM H

99K H

H 9M C

9 9M C

M H99 CM

Now we want to #ist a## the &ersons with any orders

We use the fo##owing SELE=T statement4

SELE=T 'ersonsLastName0 'ersons?irstName0 OrdersOrderNo

?AO2 'ersons

INNEA JOIN Orders

ON 'ersons'BIdOrders'BId

OADEA ;@ 'ersonsLastName

The resu#t8set wi## #oo< #i


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C !ansen O#a Timoteivn CG Sandnes

Svendson Tove ;orgvn H Sandnes

H 'ettersen ari Storgt G Stavanger

The FOrdersF ta$#e4

O*Id OrderN$ P*Id

C KM H

99K H

H 9M C

9 9M C

M H99 CM

Now we want to #ist a## the &ersons and their orders 8 if any0 from the ta$#es a$ove

We use the fo##owing SELE=T statement4

SELE=T 'ersonsLastName0 'ersons?irstName0 OrdersOrderNo

?AO2 'ersons

LE?T JOIN Orders

ON 'ersons'BIdOrders'BId




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SQL RIGT JOIN "e#w$rd

The AI6!T JOIN


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1 ,,-/

2 00,-

220/ 1

0 20/2 1

/ 0,0 1/

Now we want to list all the !ersons and their orders and all the orders with their !ersons.

#e use the followin$ %&L&'T statement

SELECT *e'sons.LastName *e'sons.F"'stName O'%e's.O'%e'No

FROM *e'sonsFULL JOIN O'%e's

ON *e'sons.*_I%O'%e's.*_I%

OR3ER &4 *e'sons.LastName

The result(set will look like this

LastName FirstName OrderNo

!ansen Ola 220/

!ansen Ola 20/2

*ette'sen +a'" ,,-/

*ette'sen +a'" 00,-

S#en%son To#e

0,0

The FULL JOIN keyword returns all the rows from the left table )Persons* and all the rows fromthe ri$ht table )Orders*. If there are rows in "Persons" that do not ha+e matches in "Orders" or ifthere are rows in "Orders" that do not ha+e matches in "Persons" those rows will be listed as

well.

SQL SET OPER+TORS


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!e SQL UNION Operator

The UNION o!erator is used to combine the result(set of two or more %&L&'T statements.

Notice that each %&L&'T statement within the UNION must ha+e the same number of columns.The columns must also ha+e similar data ty!es. ,lso the columns in each %&L&'T statement

must be in the same order.

SQL UNION Syntax

SELECT column_name(s) FROM table_name1

UNION


Note:The UNION o!erator selects only distinct +alues by default. To allow du!licate +alues use

UNION ,LL.

SQL UNION ALL Syntax


UNION 5LL


PS:The column names in the result(set of a UNION are always e-ual to the column names in the

first %&L&'T statement in the UNION.

SQL UNION Example

Look at the followin$ tables

"Employees_Norway"

E_I" E_Name

$1 !ansen Ola

$2 S#en%son To#e

$ S#en%son Ste67en

$0 *ette'sen +a'"

"Employees_USA"

E_I" E_Name


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$1 Tu'ne' Sall8

$2 +ent Cla'9

$ S#en%son Ste67en

$0 Scott Ste67en

Now we want to list all the differentem!loyees in Norway and U%,.

#e use the followin$ %&L&'T statement

SELECT E_Name FROM Em6lo8ees_No':a8

UNION

SELECT E_Name FROM Em6lo8ees_US5

The result(set will look like this

E_Name

!ansen Ola

S#en%son To#e

S#en%son Ste67en

*ette'sen +a'"

Tu'ne' Sall8

+ent Cla'9

Scott Ste67en

Note:This command cannot be used to list all em!loyees in Norway and U%,. In the eam!le

abo+e we ha+e two em!loyees with e-ual names and only one of them will be listed. TheUNION command selects only distinct +alues.

SQL UNION ALL Example

Now we want to list allem!loyees in Norway and U%,

SELECT E_Name FROM Em6lo8ees_No':a8

UNION 5LL

SELECT E_Name FROM Em6lo8ees_US5


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Result

E_Name

!ansen Ola

S#en%son To#e

S#en%son Ste67en

*ette'sen +a'"

Tu'ne' Sall8

+ent Cla'9

S#en%son Ste67en

Scott Ste67en

-iews

SQL C#EAE $IE% Statement

In %/L a +iew is a +irtual table based on the result(set of an %/L statement.

, +iew contains rows and columns 0ust like a real table. The fields in a +iew are fields from oneor more real tables in the database.

1ou can add %/L functions #2&3& and JOIN statements to a +iew and !resent the data as if

the data were comin$ from one sin$le table.

SQL C#EAE $IE% Syntax

CRE5TE ;IE< #"e:_name 5S

SELECT column_name(s)

FROM table_name

Note:, +iew always shows u!(to(date data4 The database en$ine recreates the data usin$ the

+iew5s %/L statement e+ery time a user -ueries a +iew.


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SQL C#EAE $IE% Examples

If you ha+e the Northwind database you can see that it has se+eral +iews installed by default.

The +iew "'urrent Product List" lists all acti+e !roducts )!roducts that are not discontinued*from the "Products" table. The +iew is created with the followin$ %/L

CRE5TE ;IE< =Cu''ent *'o%uct L"st> 5S

SELECT *'o%uctI3*'o%uctName

FROM *'o%ucts

#e can -uery the +iew abo+e as follows

SELECT ? FROM =Cu''ent *'o%uct L"st>

,nother +iew in the Northwind sam!le database selects e+ery !roduct in the "Products" tablewith a unit !rice hi$her than the a+era$e unit !rice

CRE5TE ;IE< =*'o%ucts 5bo#e 5#e'ae *'"ce> 5S

SELECT *'o%uctNameUn"t*'"ce

FROM *'o%ucts


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SQL Updatin& a $iew

1ou can u!date a +iew by usin$ the followin$ synta

SQL C#EAE O# #EPLACE $IE% Syntax

CRE5TE OR RE*L5CE ;IE< #"e:_name 5S

SELECT column_name(s)

FROM table_name

Now we want to add the "'ate$ory" column to the "'urrent Product List" +iew. #e will u!date

the +iew with the followin$ %/L

CRE5TE ;IE< =Cu''ent *'o%uct L"st> 5S

SELECT *'o%uctI3*'o%uctNameCateo'8

FROM *'o%ucts

SQL "roppin& a $iew

1ou can delete a +iew with the :3OP ;I command.

SQL "#OP $IE% Syntax

3RO* ;IE< #"e:_name

INDE.ES

Indexes

,n inde can be created in a table to find data more -uickly and efficiently.

The users cannot see the indees they are 0ust used to s!eed u! searches


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ON table_name (column_name)

SQL C#EAE UNIQUE IN"E' Syntax

'reates a uni-ue inde on a table. :u!licate +alues are not allowed

CRE5TE UNIUE IN3ED "n%e_nameON table_name (column_name)

Note:The synta for creatin$ indees +aries amon$st different databases. Therefore 'heck the

synta for creatin$ indees in your database.

C#EAE IN"E' Example

The %/L statement below creates an inde named "PInde" on the "LastName" column in the"Persons" table

CRE5TE IN3ED *In%e

ON *e'sons (LastName)

If you want to create an inde on a combination of columns you can list the column names

within the !arentheses se!arated by commas

CRE5TE IN3ED *In%e

ON *e'sons (LastName F"'stName)

T!e "#OP IN"E' Statement

The :3OP IN:&= statement is used to delete an inde in a table.

"#OP IN"E' Syntax (or )S A**ess+

3RO* IN3ED "n%e_name ON table_name

"#OP IN"E' Syntax (or )S SQL Ser,er+

3RO* IN3ED table_name."n%e_name

"#OP IN"E' Syntax (or "-./Ora*le+

3RO* IN3ED "n%e_name

"#OP IN"E' Syntax (or )ySQL+

5LTER T5&LE table_name 3RO* IN3ED "n%e_name

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