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Database Systems-

Principle andPractice


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[email protected]/11/18 An Introduction to DatabaseSystem

Relational Algebra

3.1 Relational Algebra(RA)

3.2 Simple and Complex Queries using RA3.3 Structure Query Language(SQL)3.4 Creating SQL Database and Tables3.5 Selecting Data

3.6 Data Insertion Updating and Deletion

Chapter Outline :


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What is relational algebra?Relational algebra is a collection ofoperations that are used to manipulate the

entire set of relations. The output of anyrelational algebra operation is always arelation.What are the Operations?

Set operations like union, intersection,difference, and Cartesian product.Selection, Projection, and Joining.

Relational Algebra


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Union )

The result of this operation, i.e. R S, is a relation thatincludes all tuples that are either in R or in S or in both.Duplicate tuples will not appear in the output.Formally: R S = { t | t R or t S }

Union Compatibility: Let R and S are two relations withattributes (A1, A2, , An) and (B1, B2, .., Bn)respectively. If R and S are to be union ed, it should satisfythe following two rules:

Rule 1: The relations R and S must have the same degree.

Rule 2: The domain of the ith attribute of R and the domainof the ith attribute of S must be same. dom (Ai) = dom (Bi), where, 1 i n.


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Example


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Relational Difference (-)

Like union, the relational differenceoperator also requires its operands to beof the same type.Format: R - SFormally: R - S = { t | t R and t S}

Semantics : Given two relations R and Sof the same type, the difference betweenthose two relations, R- S, is the relationcontaining all tuples of R that do notappear in S.

An Introduction to DatabaseSystem


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Example


Notice that Difference has a directionality to it, e.g. R-S and S-R are not the same thing.


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Intersection( )

The expression R S returns all tuplesthat appear in both the relations R andS.

Like union and difference, the relationalintersection operator requires itsoperands to be of the same type.

Formally: R S = { t | t R and t S}Derivation from existing operators:R S = R - (R - S) = S (S - R)



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Example



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Cartesian Product ()

The Cartesian product or cross-product is a binaryoperation that is used to combine two relations.Assuming R and S as relations with n and m attributesrespectively, the Cartesian product, R S can bewritten as,

R (A1, A2, , An) S (B1, B2, , Bm) The result of the above set operation is,

Q (A1, A2, , An, B1, B2, , Bm) Where,

Degree (Q) = n + mcount (Q) = Number of tuples in R * Number of tuples in S.


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Example



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Special Relational Operations-SampleRelations


SSN SNAME GPA AGE DEPARTMENTID

2007001003 CHENGLICHONG 3.33 20 31

2007001005 ZHONGWEILONG 3.62 20 33

2007001006 WUYUANLANG 4.01 20 33

2006001001 LUOZI 3.12 20 34

2006001002 GUOHUAXIAN 3.21 21 34

2006001004 LELINGBING 3.75 21

2007002001 ZHUJIANGUO 3.05 19

Figure 3.5 Student


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Figure 3.11 SC

SSN CNO GRADE

2007001003 001 78

2007001003 002 67

2007001003 003 89

2007001003 004 65

2007001005 001 75

2007001005 002 90

2007001006 002 80

2006001001 002 70

2006001001 004 90


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The SELECT operation ( )

The select operation retrieves a subset of tuples in arelation that satisfy a selection condition.

(Relation)

Query-1: Find the students whose age is 19.

The new relation created as the result of this operation consists of one tuple:

SSN SNAME GPA AGE DEPARTMENTID

2007002001 ZHUJIANGUO 3.05 19


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The SELECT operation ( )

Query-2: Select tuples (rows) of thestudent relation where the AGE is 20and Name is ZHONGWEILONG, we could

write:


)(''20

student NG ZHONGWEILOSNAME AGE


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One of the interesting properties of theselection operation is that it iscommutative. Therefore, all theexpressions shown below are equivalent,

condition-1 ( condition-2 (R))

(condition-1 AND condition-2) (R)

condition-2 ( condition-1 (R))


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The Projection Operation ( )

The projection operation is used to select only fewcolumns from a relation.

(Relation)

Query-3: List the age of all the students. age (student)

AGE

20

21

19


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Select and Project

We can perform these operations onthe relations resulting from otheroperations. To get the names ofstudents having the AGE as 20, wewrite:


))(( 20 student AGE SNAME


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Join )

Join ( )EquiJoin

Natural JoinLeft Outer JoinRight Outer JoinFull Outer Join

Theta Join


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Join )

Format: R join-condition SSemantics: Return all tuples in R S whichsatisfy the join condition.

Derivation from existing operators:R join-condition S = join-condition (R S)Format of join condition:

R.A op S.BR.A1 op S.B1 and R.A2 op S.B2 . . .


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Equijoin )

A join is called an equijoin if onlyequality operator is used in all joinconditions.

The general form for this kind of join is,

must always have = operator

21 R R y x


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Equijoin

R S R R.B = S.B SA B B C A R.B S.B C

a b b c a b b cd b c d d b b cb c a d b c c d

Most joins in practice are equijoins.


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Example



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Natural Join *)

When we omit the condition during joiningof two relations, then it is called asnatural join ( *) :

Let relations R1 has attributes(x1,x2,x3,M) andR2 has attributes(y1,y2,y3,y4,y5,M)respectively. That is ,the M attribute iscommon to the two relations. Then the natural

join of R1 and R2 is a relation withheading(x1,x2,x3,M, y1,y2,y3,y4,y5) and bodyconsisting of all tuples that the duplicatedattributed M are removed.


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Example

A B C

a 1 b 1 5

a 1 b 2 6

a 2 b 3 8

a 2 b 4 12

B E

b 1 3

b 2 7

b 3 10

b 3 2 b

5 2

R S


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Natural Join

R S

A B C E

a 1 b 1 5 3

a 1 b 2 6 7

a 2 b 3 8 10

a 2 b 3 8 2


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Theta Join ) or NonEqui Join

Let R and S are two relations. Consideran attribute x in R, and an attribute y inS. The theta join of these two relations

can be written as,

where indicates any valid relationaloperator other than =.

21 R R y x


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Theta Join

R S

A R.B C S.B E

a 1 b 1 5 b 2 7

a 1 b 1 5 b 3 10

a 1

b 2

6

b 2

7

a 1 b 2 6 b 3 10

a 2 b 3 8 b 3 10

C E


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To find all students name and selectedcourses NO, we need student and SCrelations

1.

2. We can rewrite the previous query as:


))(( .., SC STUDENT SSN SC SSN STUDENT CNOSNAME

)(, SC STUDENT CNOSNAME

Example


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Outer Joins Special Case of EquiJoin)

Usually, only a subset of tuples of each relationwill actually participate in a join, i.e. only tuplesthat match with the joining attributes. Tuples of arelation not participating in a join are calleddangling tuples .How do we keep dangling tuples in the result of a

join? Use null values to indicate a no-join situation.There are three types of outer joins

- left outer join

- right outer join and

- full outer join.


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Left outer-join R1 R2 is similar to a natural join but keep alldangling tuples of R1.Right Outer-Join R1 R2 is similar to a natural join but keep alldangling tuples of R2. Outer Join (full outer-join) R1 R2 is similar to a natural join but keep alldangling tuples of both R1 and R2.The advantages of outer join is to take the union oftuples from two relations that are not unioncompatible.


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Example:LEFT OUTER JOIN, RIGHT,OUTER JOIN



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Example:FULL OUTER JOIN



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Division

Not supported as a primitive operator, butuseful for expressing queries like:

Find students who have taken all courses .

Precondition: in A/B, the attributes in B mustbe included in the schema for A. Also, theresult has attributes A-B..


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R

S


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Examples of Division A/B

sno pnos1 p1s1 p2

s1 p3s1 p4s2 p1s2 p2

s3 p2s4 p2s4 p4

pnop2

pnop2p4

pnop1p2

p4

snos1

s2s3s4

snos1s4

snos1

A

B1B2

B3

A/B1 A/B2 A/B3


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Another Example

Another example is: Suppose we want to find all thestudents who have selected all courses (See Figure 3.19Course Table ) provided by the school.


CNO CNAME CREDIT

001 Math 3

002 Multimedia 3

003 Computer network 4

004 Software engineering 4

005 Bioinformatics 3


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We can think of it as three steps:1.We can obtain the NO. of all courses provided

by the school by:

2.We can also find all SSN, cno pairs for whichthe student has selected courses by:

3.Now we need to find all students who selectedall the courses. The divide operation providesexactly those students:


)(coursecno

)(, sccnoSSN

)()(, course sc cnocnoSSN


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3.2 Simple and Complex queries using RA



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Example

Example 1: Get supplier names forsuppliers who supply part P2:


)('2'# SP S

p pSNAME

Example 2:Get supplier names forsuppliers who supply at least one red

part:)('' P SP S read color SNAME


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CON

Example 3 :Get supplier names forsuppliers who supply all parts:

Example 4: Get supplier numbers forsuppliers who supply at least all those

parts supplied by supplier S2:


)))(((#,#

S P SP p s sname

)()( '2'##,# SP SP s s p s


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3.3 Structure Query Language SQL)

Full name of SQL --- Structural QueryLanguageOld name --- SEQUEL (Structural EnglishQUEry Language)First developed at IBM's San Jose (nowAlmaden) Research Lab. in 1974.Over 100 SQL-based products in the market.

E.g.: Oracle, Sybase, Ingres, Informix, DB2.



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Cont

The first SQL standard (SQL-86) waspublished in 1986 by ANSI. (about 100pages).SQL1 was also adopted by ISO in 1987.A major revision made in 1989 (SQL-89).The second SQL standard (SQL2) wasannounced in 1992. It has about 600

pages.The third SQL standard (SQL3) is underdiscussion. Expected release time: 20??


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Major Components of SQL

DDL --- Data Definition Language used to define tables.DML --- Data Manipulation Language (Interactive DML,ISQL) used to manipulate data directly.Embedded DML (Embedded SQL) which supports themanipulation of data from a program in a high-level

programming language.View Definition used to create different ways to look at adatabase.Authorization (DCL).Integrity Constraints which defines various constraints onthe data.

Transaction Definition which defines which group ofcommands should be treated as an atomic command.


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3.4.1 Defining Database

CREATE DATABASE

The SQL CREATE DATABASE statementis the SQL command that adds a newdatabase.A database is the outer container for

other SQL objects: tables, columns,views, indexes, etc.



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CON

The SQL CREATE DATABASE statement isused as follows:

CREATE DATABASE

Example: creates a new database namedSTUDENT_DB.

CREATE DATABASE STUDENT_DB

The CREATE DATABASE implementation and syntaxvaries substantially between different RDBMSimplementations.



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DROP DATABASE

The SQL DROP DATABASE statement isthe SQL command that removes anexisting database.

The SQL DROP DATABASE statement is usedas follows:

DROP DATABASE

The following example drops an existingdatabase named STUDENT_DB.

DROP DATABASE STUDENT_DB



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3.4.2 Defining tables and views

CREATECreate new objects (tables, views, etc.) in the

database

ALTERChange the structure of an existing object

DROPRemove the object from the database, (all its data

plus any reference to it in the data dictionary)


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CREATE TABLE

The CREATE TABLE statement is usedto create tables to store data. Integrity Constraints like primary key,unique key, foreign key can be definedfor the columns while creating the table.



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CON...

The create table statement does exactly that:

CREATE TABLE ( ,

... );

The data types that you will use most frequently areVARCHAR or CHAR for variable or fixed length strings;numeric types such as NUMBER or INTEGER; and DATEor related types. Data type syntax is variable fromsystem to system.



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Example

If we have a table for recording students information,then the columns may include information such asstudents number(SSN), name(SNAME), birthdate(BirthDate), depart number(DEPTNO).

CREATE TABLE student(SSN NUMBER NOT NULL,SNAME CHAR(10) ,BirthDate DATE ,

DEPTNO NUMBER);Note that: The NOT NULL constraint enforces the

field of SSN to always contain a value.



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ALTER TABLE

The SQL ALTER TABLE command is usedto modify the definition (structure) of atable by modifying the definition of itscolumns. The ALTER command is usedto perform the following functions.

1) Add, drop, modify table columns2) Add and drop constraints3) Enable and Disable constraints



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ADD COLUMN

To add a new columnALTER TABLE

ADD (column_name datatype);

For Example: To add a column"Address" to the student table:

ALTER TABLE student ADD Address CHAR(30);



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DROP COLUMN

To drop a columnALTER TABLE table_name DROP column_name;

For Example: To drop the column"Address" from the student table:

ALTER TABLE student DROP Address;



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MODIFY COLUMN

To modify a column

ALTER TABLE table_name MODIFYcolumn_name datatype;

For Example: To modify the columnAddress in the student table:

ALTER TABLE student

MODIFY Address CHAR(50); An Introduction to Database

System


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DROP TABLE

The DROP TABLE command allows youto destroy an existing table.

If we want to permanently remove thestudent table that we created:

DROP TABLE student


U i d D fi i Vi


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Using and Defining Views

Views provide users controlled access to tablesBase Table table containing the raw dataDynamic View

A virtual table created dynamically upon request by a userNo data actually stored; instead data from base table madeavailable to userBased on SQL SELECT statement on base tables or otherviews


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CREATE VIEW

The Syntax to create a view is

CREATE VIEW view_name ASSELECT column_listFROM table_name [WHERE condition];

The SELECT statement is used to define the columns androws that you want to display in the view


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Example

To create a view on the student table theSQL statement would be like:CREATE VIEW view_student

AS

SELECT SSN, SNAMEFROM student;Where SNAME LIKE ZHANG% With CHECK_OPTION

View has a name CHECK_OPTION works only for updateableviews and prevents updates that wouldcreate rows not included in the view


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ALTER VIEW

By the ALTER VIEW Statement we canchange the definition of a view. Thisstatement is useful to modify a view

without dropping it.

The general syntax of ALTER VIEWStatement is :

ALTER VIEW view_name [(column_list)] [WITHENCRYPTION] AS select_statement [WITH CHECKOPTION]


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Example

A one more column by the name ofAddress of student table.

ALTER VIEW view_student

ASSELECT sno, sname,AddressFROM student;


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DROP VIEW

For dropping a view you can use theDROP VIEW Statement.

The general syntax of DROP VIEWStatement is :

DROP VIEW view_name;

When view is dropped but it has no effect on the underlyingtables.

After dropping a view if you issue any query that reference adropped view then you get an error message.But dropping a table that reference any view does not dropthe view automatically. You have to dropt the view explicitly.


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Advantages of Views

Simplify query commandsAssist with data security (but don't rely on viewsfor security, there are more important securitymeasures)

Enhance programming productivityContain most current base table dataUse little storage spaceProvide customized view for user

Establish physical data independence


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Disadvantages of Views

Use processing time each time view isreferencedMay or may not be directly updateable


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Specifying constraints

Constraints offer the advantages of definingcontrols in one step during the table creationprocess (as defined by the SQL standards) andof simplifying the process to create thoseintegrity controls.

Constraints can be specified when a table iscreated

CREATE TABLE statement ALTER TABLE statement


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NOT NULL Constraint

The NOT NULL constraint enforces afield to always contain a value. Thismeans that you cannot insert a newrecord, or update a record without

adding a value to this field.The following SQL enforces the "SSN"column and the "SNAME" column to notaccept NULL values:

CREATE TABLE student(SSN NUMBER NOT NULL,SNAME CHAR(10) NOT NULL ,BirthDate DATE ,DEPTNO NUMBER);


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UNIQUE Constraint

The UNIQUE constraint uniquely identifies each record ina database table.

The following SQL creates a UNIQUE constraint on the"SSN" column when the "student" table is created:

CREATE TABLE student(SSN NUMBER NOT NULL UNIQUE,SNAME CHAR(10) NOT NULL ,BirthDate DATE ,

DEPTNO NUMBER);Note that you can have many UNIQUE constraints

per table, but only one PRIMARY KEY constraintper table.


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PRIMARY KEY Constraint

The PRIMARY KEY constraint uniquelyidentifies each record in a databasetable.

A primary key must contain uniquevalues and cannot contain NULLvalues .Each table should have a primary key,and each table can have only ONEprimary key


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CON

The following SQL creates a PRIMARY KEYon the " SSN " column when the "student " table is created:

CREATE TABLE student(SSN NUMBER PRIMARY KEY,SNAME CHAR(10) NOT NULL ,BirthDate DATE ,

DEPTNO NUMBER);


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CON

To allow naming of a PRIMARY KEYconstraint, and for defining a PRIMARYKEY constraint on multiple columns, usethe following SQL syntax:

CREATE TABLE student(SSN NUMBER NOT NULL,SNAME CHAR(10) NOT NULL ,BirthDate DATE ,DEPTNO NUMBER,

CONSTRAINT pk_studentNo PRIMARY KEY (SSN,SNAME)

);


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FOREIGN KEY Constraint

A foreign key is a referential constraint betweentwo tables. The foreign key identifies a columnor a set of columns in one (referencing) tablethat refers to a set of columns in another(referenced) table.The columns in the referencing table must bethe primary key or other candidate key in thereferenced table.The values in one row of the referencingcolumns must occur in a single row in thereferenced table.A row in the referencing table cannot containvalues that don't exist in the referenced table


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CHECK Constraint

The CHECK constraint is used to limitthe value range that can be placed in acolumn.

CREATE TABLE student(SSN NUMBER PRIMARY KEY CHECK (SSN >0),SNAME CHAR(10) NOT NULL ,BirthDate DATE ,

DEPTNO NUMBER);


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DEFAULT Constraint

The DEFAULT constraint is used to inserta default value into a column. Thedefault value will be added to all new

records, if no other value is specified.CREATE TABLE student(SSN NUMBER PRIMARY KEY CHECK(sno >0),SNAME CHAR(20) NOT NULL ,BirthDate DATE ,DEPTNO NUMBER DEFAULT 00);


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CON

The DEFAULT constraint can also be used toinsert system values, by using functions likeGETDATE():

CREATE TABLE SC

(CNO NUMBER NOT NULL,SSN NUMBER NOT NULL,GRADE NUMBER,TakeCourseDate date DEFAULT GETDATE(),

PRIMARKY KEY(SSN,CNO)FOREIGN KEY (SSN) REFERENCES student(SSN))


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Creating indexes

Indexes can be created against a table tomake searches more efficient.A book index allows you to find

information without having to readthrough the whole book.A database index enables the databaseapplication to find data quickly withouthaving to scan the whole table.


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CON

For example, if users of your application oftensearch against the name field then that field isa great candidate for an index.the CREATE INDEX command:

CREATE INDEX index_nameON table_name (column_name)

ExampleCREATE INDEX StudentIndexON student (SNAME)


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3.5 Selecting Data

Figure 3.5:student

SSN SNAME GPA AGE DEPTNO2007001003 CHENGLICHONG 3.33 20 31 2007001005 ZHONGWEILONG 3.62 20 33

2007001006 WUYUANLANG 4.01 20 33 2006001001 LUOZI 3.12 20 342006001002 GUOHUAXIAN 3.21 21 34

2006001004 LELINGBING 3.75 212007002001 ZHUJIANGUO 3.05 19


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Figure 3.19 Course

CNO CNAME CREDIT

001 Math 3002 Multimedia 3

003 Computer network 4

004 Software engineering 4

005 Bioinformatics 3


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Figure 3.11 SC

SSN CNO GRADE

2007001003 001 78

2007001003 002 67

2007001003 003 892007001003 004 65

2007001005 001 75

2007001005 002 90

2007001006 002 80

2006001001 002 702006001001 004 90


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Queries: SELECT Statement

The basic SELECT statement has three clauses:SELECT ,FROM and WHERE.SELECT: Specify the table columns that areretrievedFROM : Specify the tables accessed.WHERE: Specify which table rows are used.

The WHERE clause is optional; if missing, alltable rows are used. An asterisk ("*") can alsobe used to specify that the query should returnall columns of the queried tables.


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CON

The full syntax of the SELECT statement iscomplex as follows:

SELECT select_list

FROM table_source[ WHERE search_condition ][ GROUP BY group_by_expression ][ HAVING search_condition ]

[ ORDER BY order_expression [ ASC | DESC ] ]


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Single Table

1) Retrieve specific columns, all rows(1)Retrieve specific columns

The query retrieves a subset of columns and

all rows from a table.

[Example 1]Find the SSN, SName and GPA of all studentsselect SSN, SName, GPAfrom Student


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CON

(3)Retrieve calculated columnsThe query retrieves some columns by

computing.

[Example 3]Query the name and the birthday of

students.

Select SName,2011-AGEFrom Student


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CON

The results will be shown in Fig.21:Figure 21 Query Result of Example 3

SName (No Name)CHENGLICHONG 1990

ZHANGWEILONG 1990

Ali


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Alias

[Example 4]Select SName,2011-AGE as BirthdateFrom Student

The results will be shown in Fig.21:

SName Birthdate

CHENGLICHONG 1990

ZHANGWEILONG 1990

CON


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CON

(4)Use of DistinctThe DISTINCT keyword can be used to

return only distinct (different) values.

[Example 5]If we list the AGE of all students from the above

table.Select AGE

From Student

AGE

20

2020

20

21

21

19

CON


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CON

[Example 6]Rewriting the query as:

SELECT DISTINCT AGEFrom Students

We get the result table shown in Fig.23 with theduplicates eliminated.

AGE

20

21

19


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2). Row selection (where clause)The SQL WHERE clause is used to select data

conditionally, by adding it to already existingSQL SELECT query.

There are six basic search conditions as follows:ComparisonRangeSet membership

Pattern matchNullCompound comparison

C i h di i


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Comparison search condition

[Example 7]If we want to select all students from our

database table, having AGE 20 we need touse the following SQL syntax:

Select * from Student where AGE=20

SSN SNAME GPA AGE DEPTNO

2007001003 CHENGLICHONG 3.33 20 31

2007001005 ZHONGWEILONG 3.62 20 33 2007001006 WUYUANLANG 4.01 20 33 2006001001 LUOZI 3.12 20 34


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[Example 9]We would use the negated version to

retrieve any members of students with a

GPA outside between 3 and 3.5 as:Select *From studentWhere GPA NOT BETWEEN 3 AND 3.5

Set membership search


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pcondition(IN/NOT IN)

The set membership search condition IN allowsyou to specify multiple values in a WHEREclause.It tests whether a data value matches one of a

list values.

[Example 10]We want to select the students with an AGE

equal to 19 or 20 in the table above.Select * from studentWhere AGE IN (19, 20)


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2007001003 CHENGLICHONG 3.33 20 31

2007001005 ZHONGWEILONG 3.62 2033

2007001006 WUYUANLANG 4.01 20 33

2006001001 LUOZI 3.12 20 34

2007002001 ZHUJIANGUO 3.05 19

The operator NOT IN can be used to check for datavalues that dont lie in a specific list of values.

Figure 25 Query Result of Example 10

Pattern match search


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condition(LIKE/NOT LIKE)

The LIKE operator allows you create aSQL query that performs inexact patternmatching through the use of wildcard

characters.The % wildcard matches zero or morecharacters of any type.The _ wildcard matches exactly onecharacter of any type.


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CON


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CON...

[Example 12]To match all strings that end with

'ZHANG', the pattern would look like:

'%zhang':SELECT SNAMEFROM STUDENTWHERE SNAME LIKE '%zhang';

CON


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CON...

[Example 13]To match all strings where the word

'zhang' occurs somewhere: '%zhang%':

SELECT SNAMEFROM STUDENTWHERE SNAME LIKE '%zhang%';

CON


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CON...

[Example 14]To match strings with that begin with

zhang consisting of exactly eight

characters zhang _ _ _ SELECT SNAMEFROM STUDENTWHERE SNAME LIKE 'zhang _ _ _;

CON


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CON...

[Example 15]To match strings that there are must be

exactly four characters in the string, the

END of which must be an _ _ _ g SELECT SNAMEFROM STUDENTWHERE SNAME LIKE ' _ _ _g;

CON


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CON...

[Example 16]To match strings that there are at least one

character between 'a' and 'c' a_%c SELECT SNAMEFROM STUDENTWHERE SNAME LIKE 'a_%c';

If the search strings can include thewildcards(%,_) itself, we can use an escapecharacter to represent the wildcards.

For example, to match the string 20%, we canuse :

Like 20#% ESCAPE #

NULL search condition


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NULL search condition

The operator NULL means the data valuefor the column is unknown or notavailable.

NULL is not synonymous withzero (numeric or binary value)a zero-length string,

blank (character value)

CON


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CON...

Suppose that the "DEPTNO" column in the"STUDENT" table is optional. This means that ifwe insert a record with no value for the "DEPTNO " column, the " DEPTNO " column willbe saved with a NULL value.

We can select only the records with NULLvalues in the " DEPTNO " column by using theIS NULL operator:

[Example 17]SELECT * FROM studentWHERE DEPTNO IS NULL

CON


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CON...

[Example 18]If we select only the records with no NULL

values in the " DEPTNO " column, we

will have to use the IS NOT NULLoperator:SELECT * FROM studentWHERE DEPTNO IS NOT NULL

Compound search condition


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Compound search condition

The AND & OR operators are used to filterrecords based on more than onecondition.

The AND operator displays a record ifboth the first condition and the secondcondition is true.The OR operator displays a record ifeither the first condition or the secondcondition is true.

CON


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CON...

[Example 19]If we want to select only the persons with

AGE equal to "20" AND GPA greater

than "3", we use the following SELECTstatement:SELECT *FROM student

WHERE AGE=20 AND GPA>3.5

Sorting Results (Order by Clause )


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Sorting Results (Order by Clause )

SQL ORDER BY clause is used to sort the result-set by aspecified column or more columns.

[Example 20]If we want to sort our Users table by the GPA column, we

have to use the following ORDER BY SQL statement:SELECT * FROM studentORDER BY GPA

If you want to sort the records in a descending

order, you can use the DESC keyword.

CON


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CON...

[Example 21]Now we want to select all the persons

from the table above, however, we want

to sort the AGE descending by their lastname.SELECT *FROM studentORDER BY AGE DESC


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COUNT function


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COUNT function

The COUNT function counts the number of rowsin a table, or the number of distinct values fora given column. It can operate, therefore, atthe column or row level.

[Example 22]To count the number of students names in the

Student table :SELECT COUNT(SNAME)FROM Student

CON


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CON...

[Example 23]To count the number of distinct students names

represented in the students table, issue the following:SELECT COUNT(DISTINCT SNAME)FROM Student

The keyword DISTINCT is not considered an argument ofthe function. It simply specifies an operation to beperformed before the function is applied. WhenDISTINCT is coded, duplicate values are eliminated.If DISTINCT is not specified, then ALL is implicitlyspecified. ALL also can be explicitly specified in theCOUNT function. When ALL is specified, duplicate valuesare not eliminated.

AVG function


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AVG function

The AVG function computes the averageof the values for the column orexpression specified as an argument.This function operates only on numericarguments.

[Example 24]The following example calculates the

average GPA of the students table:SELECT AVG(GPA)FROM Student

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CON...

[Example 25]If you want to get the average GPA for a

particular set Students you can do it this

way:SELECT AVG(GPA)FROM StudentWHERE DEPTNO=33


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CON


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CON...

The MAX function returns the largestvalue in the specified column orexpression.

[Example 27]The following SQL statement determines

the largest GPA :SELECT MAX(GPA)FROM Student

CON...


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CON...

[Example 28]It returns the highest GPA belongs to a

student in DEPTNO 32:

SELECT MAX(GPA)FROM studentWHERE DEPTNO=32

SUM function


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SUM function

The accumulated total of all values in thespecified column or expression arereturned by the SUM column function.

[Example 29]For example, the following SQL statement

calculates the total GPA for thestudents:

SELECT SUM(GPA)FROM Student

GROUP BY


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GROUP BY

The GROUP BY statement is used inconjunction with the aggregatefunctions to group the result-set by oneor more columns.SQL GROUP BY Syntax

SELECT column_name, aggregate_function(column_name)FROM table_name

WHERE column_name operator valueGROUP BY column_name

CON...


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CON...

[Example 30]Want to find the average grade of each

student.

SELECT Avg(grade)FROM SCGROUP BY SSN

HAVING Clause


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HAVING Clause

The HAVING clause was added to SQLbecause the WHERE keyword could notbe used with aggregate functions.

SQL HAVING Syntax:

SELECT column_name, aggregate_function(column_name)FROM table_nameWHERE column_name operator valueGROUP BY column_nameHAVING aggregate_function(column_name) operator value

CON...


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CON...

[Example 31]Now we want to find if any of the

students have an average grade of

more than 81.

SELECT Avg(grade)FROM student

GROUP BY SSNHAVING Avg(grade)>80

CON...


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CON...

[Example 32]Now we want to find if the students

"2007001006" or "2006001001" have

an average grade of less than 81.

SELECT SSN,Avg(grade)FROM student

WHERE SSN='2007001006' OR SSN =2006001001GROUP BY SSNHAVING Avg(grade)


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functions1). Aggregate functions can be executed only in SELECT

statements.2). An aggregate function must be specified for an

explicitly named column or expression.3). Each aggregate function returns only one value for the

set of selected rows.4). If you apply an aggregate function to one column in a

SELECT statement, you must apply column functions toany other columns specified in the same SELECTstatement, unless you also use the GROUP BY clause.

5). Use GROUP BY to apply an aggregate function to agroup of named columns. Any other column named inthe SELECT statement must be operated on by anaggregate function.

CON...


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CO ...

6). When using the AVG, MAX, MIN and SUM functions onnullable columns, all occurrences of NULL are eliminatedbefore applying the function.

7). You can use the DISTINCT keyword with all aggregatefunctions to eliminate duplicates before applying the

given function. DISTINCT has no effect, however, on theMAX and MIN functions.

8). You can use the ALL keyword to indicate that duplicatesshould not be eliminated. ALL is the default.

9). An aggregate function can be specified in a WHEREclause only if that clause is part of a sub query of aHAVING clause. Additionally, every column namespecified in the expression of the aggregate functionmust be a correlated reference to the same group.

Multiple Tables


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p

SQL allows us to query multiple tables inone SELECT-FROM-WHERE statement.The SELECT and WHERE can refer to the

attributes of any of the tables once welist each table in the FROM clause.ANSI standard SQL specifies four typesof JOINs: INNER, OUTER, LEFT, andRIGHT.a table (base table, view, or joinedtable) can JOIN to itself in a self-join.

CON...


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2007001003 CHENGLICHONG 20 31

2007001005 ZHONGWEILONG 20 33

2007001006 WUYUANLANG 4.01 20 33

2006001001 LUOZI 3.12 20 34

2006001001 GUOHUAXIAN 3.21 21 34

2007002001 ZHUJIANGUO 19

CON...


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Note: The " Life Science " Department currentlyhas no listed students. Also, student "ZHUJIANGUO " has not been assigned to anyDepartment yet.

DEPTNO DEPTNAME

31 Computer Science

33 Information Engineering

34 Civil Engineering

35 Life Science

INNER JOIN


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Inner join creates a new result table bycombining column values of two tables(A and B) based upon the join-predicate. The query compares each row of A with eachrow of B to find all pairs of rows which satisfythe join-predicate.When the join-predicate is satisfied, columnvalues for each matched pair of rows of A andB are combined into a result row.

CON...


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The "implicit join notation" simply liststhe tables for joining (in the FROMclause of the SELECT statement), usingcommas to separate them.It specifies a cross-join, and the WHEREclause may apply additional filter-predicates (which function comparably

to the join-predicates in the explicitnotation).

CON...


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[Example 33]The following example shows a query

using the inner join statement:

SELECT *FROM student, departmentWHERE student.DeptID =

department.DeptID

CON...


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Student.

SSN

Student.SNA

ME

Student.

GPA

Student.

AGE

Student.D

EPTID

Department.D

EPTID

Department.DEP

TNAME2007001003

CHENGLICHONG

20 31 31 ComputerScience

2007001005

ZHONGWEILONG

20 33 33 InformationEngineering

2007001006

WUYUANLANG

4.01 20 33 33 InformationEngineering

2006001001

LUOZI 3.12 20 34 34 CivilEngineering

200600

1001

GUOHUAXI

AN

3.21 21 34 34 Civil

Engineering

OUTER JOIN


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The OUTER JOIN clause differs from thestandard JOIN clause (also known asthe INNER JOIN clause) in that rows arereturned even when there are nomatches through the JOIN critieria.LEFT OUTER JOINRIGHT OUTER JOINFULL OUTER JOIN

LEFT OUTER JOIN


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Select all the rows from the first tablelisted after the FROM clause, no matterif they have matches in the secondtable.

[Example 33]If we slightly modify our last SQL statement to:

SELECT *

FROM student LEFT OUTER JOIN departmentON student.DEPTID = department.DEPTID

CON...


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Student.

SSN

Student.SNA

ME

Student.

GPA

Student.

AGE

Student.D

EPTID

Department.D

EPTID

Department.DEP

TNAME

200700

1003

CHENGLIC

HONG

20 31 31 Computer

Science

200700

1005

ZHONGWEI

LONG

20 33 33 Information

Engineering200700

1006

WUYUANL

ANG

4.01 20 33 33 Information

Engineering

200600

1001

LUOZI 3.12 20 34 34 Civil

Engineering200600

1001

GUOHUAXI

AN

3.21 21 34 34 Civil

Engineering

200700

2001

ZHUJIANG

UO

19

RIGHT OUTER JOIN


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The RIGHT OUTER JOIN returns all rowsfrom the second table.

[Example 34]For example, this allows us to find each student and his or

her department, but still show departments that have nostudent.

SELECT *FROM student RIGHT OUTER JOIN department

ON student.DEPTID = department. DEPTID;

CON...


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Student.SSN

Student.SNAME

Student.GPA

Student.AGE

Student.DEPTID

Department.DEPTID

Department.DEPT NAME

2007001003

CHENGLICHONG

20 31 31 Computer Science

2007001005

ZHONGWEILONG

20 33 33 InformationEngineering

2007001006

WUYUANLA NG

4.01 20 33 33 InformationEngineering

2006001001

LUOZI 3.12 20 34 34 Civil Engineering

2006001001

GUOHUAXIA N

3.21 21 34 34 Civil Engineering

35 Life Science


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Student.S Student.SNAM Student.G Student.A Stude Departm Department.DEPT


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SN E PA GE nt.

DEPT

ID

ent.

DEPTID

NAME

20070010

03

CHENGLICH

ONG

20 31 31 Computer Science

20070010

05

ZHONGWEIL

ONG

20 33 33 Information

Engineering20070010

06

WUYUANLA

NG

4.01 20 33 33 Information

Engineering

20060010

01

LUOZI 3.12 20 34 34 Civil Engineering

20060010

01

GUOHUAXIA

N

3.21 21 34 34 Civil Engineering

35 Life Science

20070020

01

ZHUJIANGU

O

19


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Cont


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[Example 37] : Find all pairs of studentswho have the same GPA.

select s1.SID, s2.SID

from Students s1, Students s2where s1.GPA = s2.GPA

and s1.SID < s2.SID

JOIN A TABLE TO ITSELF


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[Example 38] : Find the names of allstudents whose GPA is higher thanCHENSHI 's GPA.

select s1.SNamefrom Student s1, Student s2where s2.SName = 'CHENGSHI'

and s1.GPA > s2.GPA

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[Example 39] Find the names and GPAs of allstudents who take database systems.

select SName, GPA from Student, sc, Course

where cname= `DBS and Student.ssn = sc.ssnand sc.cno= Course.cn

Set Operation :Union Intersect& Minus


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& Minus

SQL supports three set operations:union, intersect, minusUnion compatibility is required.

Consider the following two relations:G_Students(ssn, Name, GPA, GRE, Dept_Name)Instructors(ssn, Name, Office, Salary, Dept_Name)

Union


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[Example 40]: Find the names of thosepeople who are either select lesson21001001 or lesson 22003002

(select SName from studentwhere ssn=any (select ssn from scwhere cno=21001001) )

union(select SName from students

where ssn=any (select ssn from scwhere cno=22003002) )

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union removes duplicate rows.union all keeps duplicate rows.

Set Operation: Intersect


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[Example 41] : Find the names of thosepeople who a select lesson21001001 and lesson 22003002 (select SName from student


intersect(select SName from student


Set Operation: Minus


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[Example 42]: : Find the names of thosewho select lesson 21001001 but hasnot select the lesson 22003002

(select SName from studentwhere ssn=any (select ssn from sc

where cno=21001001) )minus(select SName from student


Set Operation: IN & NOT IN


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[Example 43]: : Find all students whoare 20, 21, or 19 years old.

select * from Student

where Age in (19, 20, 21)

NOT IN is the opposite of IN.

Sub queries


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A subquery is a SELECT statement that isnested within another SQL statement.Return any number of values

Can be found in, the column list of aSELECT statement, a FROM, GROUP BY,HAVING, and/or ORDER BY clauses of aSQL statement.

CON


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[Example 48]To find the names of every student who studies in the

same department as a person called Jones .

SELECT SNAMEFROM studentWHERE DEPTNO =

(SELECT DEPTNOFROM student

WHERE SNAME = 'JONES')

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Or as a join statement, like this:

SELECT e1. SNAME

FROM student e1,student e2WHERE e1. DEPTNO = e2. DEPTNO

AND e2. SNAME = 'JONES'

CON


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[Example 49]: Find the names of allstudents who take at least onecourse titled multimedia.select sNamefrom Student s, SC ewhere s.ssn = e.ssn and e.cno in

(select cno from Coursewhere Cname = ' multimedia')

Nesting levels


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SELECT select-listFROM .........WHERE (select-field1, select-

field2,.........)comparison operator

(SELECT select-list2

FROM........WHERE (..........))

comparison-operator:


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ALL -- the comparison must be true forall returned values.ANY -- The comparison need only betrue for one returned value.IN may be used in place of = ANY.NOT IN may be used in place of !=ALL.

Cont


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The previous query is a nestedquery.The query outside is an outer queryand the query nested under theouter query is an inner query.Multiple nesting's are allowed.The semantics of the above query isto evaluate the inner query first andevaluate the outer query last.Many nested queries haveequivalent non-nested versions.

Non Nested Equivalent


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The previous query is equivalent to: (1)

select SName

from Student s, sc e, Course cwhere s.ssn = e.ssnand e.cno= c.cno and c.cname =multimedia'

Cont


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(2)select SNamefrom Student where ssn in

(select ssn from scwhere Cno in(select Cno from Course

where cname = multimidea'))

Correlated Query


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Definition: If some attributes of arelation declared in the from clause ofan outer query are referenced in thewhere clause of an inner query, then thetwo queries are said to be correlated,and the inner query is called acorrelated inner query.

CON


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[Example 50]:Find the names of all students who has NOT select a

Course with CNO=1.

SELECT Sname

FROMStudentWHERE NOT EXISTS

(SELECT *

FROM SC

WHERE SSN =Student.SSN AND Cno=1)

Cont


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Evaluation of correlated queries: for eachtuple in the outer query, evaluate theinner query once.

The scoping rule of attribute names:select ... from R1, ..., Rk where ...

(select ... from S1, ..., Smwhere S1.A = R2.B and C = D and ... )(1) If attribute C is not an attribute in S1,

..., Sm, and C is an attribute in some Ri,then C = Ri.C.

(2) If C is in both Sj and Ri, then C = Sj.C.

Cont


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[Example 51]: : Find the names of thosestudents who are 18 or younger andwhose GPA is higher than the GPA ofsome students who are 20 or older.

select sName from Studentwhere Age some(select GPA from Studentwhere Age >= 20)

Other set comparison operators:


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any, all,


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[Example 52]: Find all students whotake at least one course.

select * from Student s where exists

(select * from scWhere ssn= s.ssn)


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Cont


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The previous query is equivalent to: (1) select s.*

from Student s, sc e

where s.SID = e.SID(2) select * from Student where ssn in

(select ssn from sc)

Cont


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[Example 53]: Find all students who donot take 21003001 .

select * from Student s where not exists(select * from scwhere ssn= s.ssnand Cno = '21003001.')This query is equivalent to:

select * from Student where ssn not in(select ssn from scwhere Cno = '21003001.')


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[Example 54]:Find the names of all students who study in thesame department with a student with sname=liucheng . SELECT ssn Sname DEPTNO

FROM Student S1WHERE EXISTS

SELECT *FROM Student S2WHERE S2.DEPTNO = S1.DEPTNO AND

S2.Sname = liucheng '

Cont


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[Example 55]: Find all the students whotake all courses select * from Student swhere not exists

(select * from Course cwhere not exists

(select * from sc

where ssn= s.ssnand Cno = c.Cno))

Cont


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[Example 56] : Find the names and GPAs ofthose students who take all courses takenby a student with SID = 2006002001.

select Name, GPA from Student swhere not exists

(select * from Course cwhere Cno in(select Cno from scwhere ssn= 2006002001) and not exists

(select * from sc ewhere ssn=e.ssn and Cno =

c.Cno))

Scalar Functions of DB2


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Scalar functions are applied to a columnor expression and operate on a singlevalue.The result of a scalar function is a transformedversion of the column or expression beingoperated on.The transformation of the value is based onthe scalar function being applied and the value

itself.

Cont


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TRUNCATE or TRUNC Converts the first numeric argument by truncating it to the

right of the decimal place by the integer numberspecified in the second numeric argument.

[Example 34]

SELECT TRUNC(3.014015,2)FROM SYSIBM.SYSDUMMY1;

This SQL statement returns the number 3.010000, becausethe second argument specified that only 2 significantdigits are required. The rest was truncated.

Cont


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ROUNDRounds the first numeric argument to the

number of places specified in the secondargument.

UPPER or UCASEConverts a character string into all uppercase

characters LOWER or LCASE

Converts a character string into all lowercasecharacters.

Cont


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SUBSTRReturns the specified portion of a character column from

any starting point to any ending point.[Example 45]SNAME is a CHAR(20) column in sample table STUDENT.

When SNAME has the value ZHONGWEILONG: Function: Returns:

-----------------------------------SUBSTR(SNAME,2,3) -- 'HON'SUBSTR(SNAME,2) -- ' HONGWEILONG'

SUBSTR(SNAME,2,12) -- ' HONGWEILONG ' followed by one blankSUBSTR(SNAME,13) -- a zero-length stringSUBSTR(SNAME,13,4) -- four blanks

Cont


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LTRIMThe LTRIM function removes blanks or

hexadecimal zeros from the beginning ofa string expression.

RTRIMThe RTRIM function removes blanks or

hexadecimal zeros from the end of astring expression.

Cont


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CHARThe CHAR function returns a fixed-length

character string representation of theargument .

[Example 46]SELECT CHAR(CURRENT DATE)

CURRENT DATE is a DATE type which displays current datetime of the system server. When it represents the date15 March 2011, the example returns the string value'3/15/2011 in character string .

Cont


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CONCATThe CONCAT function combines two compatible

string arguments.[Example 47]Using sample table DSN8910.EMP, concatenate

column FIRSTNME with column LASTNAME.Both columns are defined as varying-lengthcharacter strings.

SELECT CONCAT(FIRSTNME, LASTNAME)FROM DSN8910.EMP;

Cont


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WEEK The WEEK function returns an integer in the

range of 1 to 54 that represents the week ofthe year. The week starts with Sunday, and

January 1 is always in the first week. DAY

The DAY function returns the day part of a value.If the argument is a date, timestamp, or string

representation of either, the result is the daypart of the value, which is an integer between1 and 31

Cont


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DATEThe DATE function converts a value representing

a date to a DB2 date. The value to beconverted can be a DB2 timestamp, a DB2

date, a positive integer, or a character string.MONTH

The MONTH function returns the month part of avalue. If the argument is a date, timestamp, or

string representation of either, the result is themonth part of the value, which is an integerbetween 1 and 12.

Cont


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TIMEThe TIME function Converts a value representing

a valid time to a DB2 time. The value to beconverted can be a DB2 timestamp, a DB2

time, or a character string.

YEAR The YEAR function returns the year part of a

l th t i h t g hi t i g Th

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