PART 2 RELATIONAL DATABASES. Chapter 4 Advanced SQL

PART 2

RELATIONAL DATABASES

Chapter 4

Advanced SQL

April 2008 Database System Concepts - Chapter4 Advanced SQL - 3

Integrity constraints in SQL §4.1-4.2

Security in SQL (§4.3) authorization, grant/revoke

Embedded and dynamic SQL §4.4-4.5

Three Parts in Chapter 4


Case study used in this chapter

return

Three Parts in Chapter 4 (cont.)


4.1.1 Built-in Data Types in SQL In addition to the basic data types, e.g. char(n), varchar(n), int,

smallint, numeric(p, d), real, double precision, float(n), described in §3.2, the other built-in data types include

date: Dates, containing a (4 digit) year, month and date e.g. date ‘2005-7-27

time: Time of day, in hours, minutes and seconds e.g. time ‘09:00:30.75

timestamp: date plus time of day e.g. timestamp ‘2005-7-27 09:00:30.75’

interval: period of time e.g. interval ‘1’ day

§4.1 SQL Data Types and Schemas


Subtracting a date/time/timestamp value from another gives an interval value

interval values can be added to date/time/timestamp values

Values of individual fields can be extracted from date/time/timestamp

e.g. extract (year from r.starttime) We can cast /convert string types to date/time/timestamp

e.g. cast <string-valued-expression> as date e.g. cast <string-valued-expression> as time

4.1.1 Built-in Data Types in SQL (cont.)


The create type clause can be used to define new user-defined types

e.g. create type Dollars as numeric (12,2) final The create domain clause can be used to define new user-

defined domains e.g. create domain person_name char(20) not null

4.1.2 User-defined Types


4.1.3 Large-Object Types Large objects (photos, videos, CAD files, etc.) are stored as a

large object blob: binary large object

the object is a large collection of uninterpreted binary data, whose interpretation is left to an application outside of the database system

clob: character large object the object is a large collection of character data

When a query returns a large object, a pointer is returned rather than the large object itself.


E.g.

book_view clob(10KB)

image blob(10MB)

movie blob(2GB)

4.1.3 Large-Object Types (cont.)


How to name the relations in DB, or how to specify the names of the relations in DB

The three-level hierarchy for naming relations catalogs, each of which can contain schemas;

The catalog is also called database schemas, in which the relations and views are stored relations and views e.g. a three-part name for the relation

catalog5.bank_schema.account SQL environments, including

connection, catalog, schema, user identifier

4.1.4 Schemas, Catalogs, and Environments


§4.2 Integrity Constraints

Integrity constraints guard against accidental damage to the database, by ensuring that authorized changes to the database do not result in a loss of data consistency

Classification of integrity constraints and some examples refer to Fig.4.0.1

attribute-level tuple-level relation-level

static data type data format,

e.g. YY.MM.DD domain constraints,

e.g.1 null value

constraints among attributes

values e.g.2 mapping

cardinality constraints

entity integrity e.g.3 referential

integrity (§4.2.5) functional

dependency (§7) statistical constraints e.g.6

dynamic

constraints on

updating of

attribute values or attribute definition e.g.4

constraints among attributes values e.g.5

transaction constraint: atomy, consistency, isolation, durability

(§ 15, 16, 17)

Fig.4.0.1


E.g.1 “ the salary of manager should not be lower than $1000” in Employee

E.g.2 table T (x, y, z ), z =x+y, z is a derived attributes from x and y.

E.g.3 “the student# for table student should not be null” E.g.4 ”the age of students should only be added” E.g.5 when employee tuples is modified, new.sal > old.sal +

0.5*age E.g.6 statistical constraints: in table employee , “the salary

of manager should be four times more than that of workers”

Some Examples of Integrity Constraints


An SQL relation is defined using the create table command

create table r (A1 D1, A2 D2, ..., An Dn,(integrity-constraint1), ...,(integrity-constraintk))

r is the name of the relation each Ai is an attribute name in the schema of relation r

Di is the data type of values in the domain of attribute Ai

4.2.1-4 Constraints on a Single Relation


The allowed integrity constraints include primary key not null Unique foreign keys check (P ), where P is a predicate

Not Null Constraints e.g.1 Declare branch_name for branch is not null

branch_name char(15) not null e.g.2 Declare the domain Dollars to be not null

create domain Dollars numeric(12,2) not null

4.2.1-4 Constraints on a Single Relation (cont.)


The Unique Constraint is as follows

unique ( A1, A2, …, Am) it states that the attributes

A1, A2, … Am form a candidate key

candidate keys are permitted to be null (in contrast to primary keys)

e.g. create table customer(customer-id char(15) customer-name char(15)

customer-city char(30), primary key (customer-id)

unique (customer-name)



The check clause is applied to relation declaration as well as to domain declaration

check (P ), where P is a predicate E.g. Declare branch_name as the primary key for branch and

ensure that the values of assets are non-negative create table branch

(branch_name char(15), branch_city char(30), assets integer, primary key (branch_name), check (assets >= 0))



E.g. if “Perryridge” is a branch name appearing in one of the tuples in the account relation, then there exists a tuple in the branch relation for branch “Perryridge”

Referential Integrity ( 关联 / 参照完整性 ) ensures that a value that appears in one relation for a given

set of attributes also appears for a certain set of attributes in another relation

4.2.5 Referential Integrity


The primary key, candidate keys and foreign keys can be specified as parts of the SQL create table statement:

the primary key clause lists attributes that comprise the primary key.

the unique key clause lists attributes that comprise a candidate key.

the foreign key clause lists the attributes that comprise the foreign key and the name of the relation referenced by the foreign key. By default, a foreign key references the primary key attributes of the referenced table.

4.2.5 Referential Integrity (cont.)


Definition of referential integrity Let r1(R1) and r2(R2) be relations with primary keys K1 and K2

respectively, refer to Fig. 4.0.2 e.g. branch(branch-name, branch-city, assets),

account(account-number, branch-name, balance)

the subset of R2 (e.g. branch-name) is a foreign key (from

r2, e.g. account) referencing K1 in relation r1 (e.g. branch) , if for every t2 in r2 there must be a tuple t1 in r1 such that t1[K1] = t2[]

note: = K1 R2 ⊆



referential integrity constraint also called subset dependency since its can be written as (r2) K1 (r1)

e.g. branch-name (account) branch-name (branch)

a foreign key of table r2 references the primary key attributes K1 of the referenced table r1

A good DB design should ensures that any relation schema R2 (and its any tuples) can only reference other relation schema R1 through its foreign key


K1 A2 A3

Perryridge Perryridge 1200

New-York New-York 5000

Brooklyn Brooklyn 3000

Los-Angles Los-Angles

2500

Austin Austin 1800

K2 B3

101 Perryridge 200

102 Perryridge 400

201 New-York 500

203 New-York 1000

303 Brooklyn 400

401 Los-Angles 600

Fig. 4.0.2

r1(R1), e.g. branch r2(R2), e.g. account

branch (branch-name, branch-city, assets) Account

(account-number, branch-name, balance)


create table branch (branch_name char(15), branch_city char(30), assets numeric(12,2), primary key (branch_name ))

create table account(account_number char(10),branch_name char(15),balance integer,primary key (account_number), foreign key (branch_name) references branch )

Referential Integrity in SQL – Example


For a many to many relationship set R between entity sets E1 and E2 in Fig. 4.0.3, the reduced relational schema R for Re includes the primary keys K1 of E1 and K2 of E2, then K1 and K2 form foreign keys of R referencing R1 and R2 respectively

ReE1 E2

R1(K1 ,…, ) R2(K2 , …, )

R(K1, K2 , …, )

Fig. 4.0.3



Weak entity sets are also a source of referential integrity constraints

e.g. payment (loan-number, payment-number, date, amount)

Fig.4.0.4 E-R diagram with a weak entity set

manyone

total E1E2



Assuming a foreign key of table r2 references the primary key attributes K of the referenced table r1

An example, as shown in Fig.4.0.2 r1 (R1) : branch (branch-name, branch-city, assets )

r2 (R2) : account (account-number, branch-name, balance) : branch-name t1 = (New-York-branch , New York , $2000) in r1

t2 = (201#, New-York-branch, $500) in r2

Database Modification


When the DB is modified by Insert, Delete, and Update, the tests must be made in order to preserve the following referential integrity constraint:

(r2) K (r1)


E.g. insert t2 = (303#, Brooklyn-branch, $400) into account, t1= (Brooklyn-branch , * , *) exists in branch ?

e.g. t2 []=“Brooklyn-branch” branch-name (branch)

/*新插入的 account的开户行是否已在 branch中存在？

For more details, refer to Appendix A

Database Modification (cont.)


An assertion is a predicate expressing a condition that we wish the database always to satisfy e.g. domain constraints, referential-integrity constraint

An assertion in SQL takes the form

create assertion <assertion-name> check <predicate>

When an assertion is made, the DBMS tests it for validity. Any modification to DB is allowed only if it does not cause that assertion to be violated this testing may introduce a significant amount of overhead,

hence assertions should be used with great care

§4.2.6 Assertions ( 断言 )


E.g. The sum of all loan amounts for each branch must be less than the sum of all account balances at the branch.

create assertion sum-constraint check (not exists (select * from branch

where (select sum(amount) from loan where loan.branch-name =

branch.branch-name) >= (select sum(amount) from account

where loan.branch-name = branch.branch-name)))

分行存款总额

分行借款总额

§4.2.6 Assertions (cont.)


§4.3 Authorization

Forms of authorization on parts of the database include read, insert, update, delete

Forms of authorization to modify the database schema (covered

in Chapter 8) index resources - allows creation of new relations alteration - allows addition or deletion of attributes in a

relation drop - allows deletion of relations.


Authorization Specification in SQL The grant statement is used to confer authorization

grant <privilege list>

on <relation name or view name> to <user list>

<user list> is: a user-id public, which allows all valid users the privilege granted A role (more on this in Chapter 8)

Granting a privilege on a view does not imply granting any privileges on the underlying relations.

The grantor of the privilege must already hold the privilege on the specified item (or be the database administrator).


Privileges in SQL

select: allows read access to relation,or the ability to query using the view

example: grant users U1, U2, and U3 select authorization on the branch relation:

grant select on branch to U1, U2, U3

insert: the ability to insert tuples update: the ability to update using the SQL update statement delete: the ability to delete tuples. all privileges: used as a short form for all the allowable privileges more in Chapter 8


Revoking Authorization in SQL The revoke statement is used to revoke authorization.

revoke <privilege list>

on <relation name or view name> from <user list> Example:

revoke select on branch from U1, U2, U3

<privilege-list> may be all to revoke all privileges the revokee may hold.

If <revokee-list> includes public, all users lose the privilege except those granted it explicitly.


Revoking Authorization in SQL (cont.)

If the same privilege was granted twice to the same user by different grantees, the user may retain the privilege after the revocation.

All privileges that depend on the privilege being revoked are also revoked.


§4.4 Embedded SQL

Four approaches to take SQL as DB query tools interactive SQL

SQL is used directly as DML and DDL through DBS human-machine interfaces

embedded SQL SQL is embedded in general-purpose programming

languages C language executing of general-purpose programming language

programs with SQL statement embedded results in DB access


§4.4 Embedded SQL (cont.)

dynamic SQL: ODBC/JDBC as general-purpose API in client-server DBS environments, the client

application program, which is written in C or Java language and located at client-sites, calls ODBC or JDBC API in which SQL query statements are included, to access the DB locating at server-site

as the general-purpose API, independent of DBMS e.g. SQLExecDirect(hstmt, "SELECT * FROM

authors", Len(SQLstmt))


the SQL query statements are included in the API e.g. MySQL API, refer to Appendix K for more details

§4.4 Embedded SQL (cont.)


4.4.1 Embedding SQL in Host Language Programs

The SQL standard defines embeddings of SQL in a variety of programming languages such as C, Pascal, Fortran, and Cobol

A language to which SQL queries are embedded is referred to as a host language( 宿主语言 ), and the SQL structures permitted in the host language comprise embedded SQL

Merits of embedded SQL 交互式 SQL 只能进行 DB 的访问操作，不能对 DB 访问

结果进行进一步的数据处理 Embedded SQL 将 SQL 的数据库访问功能与 C 语言等宿

主语言的数据处理能力相结合，提高了数据应用系统的能力


A program with embedded SQL consists of two parts, the program declaration part and the program execution part.

In program declaration part, shared variables are defined, the host language statements SQL statements in the program exchange data through the shared variables

In host programs, shared variables are declared as, e.g. EXEC SQL BEGIN DECLARE SECTION

int amount;

EXEC SQL END DECLARE SECTION

4.4.1 Embedding SQL in Host Language Programs (cont.)


In program execution part, SQL statements are embedded in host language programs as

EXEC SQL <embedded SQL statement > END-EXEC note: this varies by language. e.g. the Java embedding uses

# SQL { …. } E.g.1 From within C language, find the names and cities of

customers with more than the variable amount ( input from screen by users) dollars in some account

/* 找出所有在银行有“存款额大于 amount” 的帐户的客户的姓名和所在城市

amount is the shared variable defined in the declaration part



the C program is as follows EXEC SQL BEGIN DECLARE SECTION

int amount; EXEC SQL END DECLARE SECTION amount := input-from-screen-by-users EXEC SQL select customer-name, customer-city

from depositor, customer, accountwhere depositor.customer-name = customer.customer-name and depositor account-number = account.account- number and account.balance > :amount

END-EXEC

shared variable defined in host language



/* 利用 Embedded SQL 进行查询时，查询结果有可能包括多个元组，此时无法直接将多个元组通过共享变量赋值传递给宿主程序

/* 系统开辟专门 working 区域存放 SQL 查询的结果关系，并利用查询游标 c 指向此区域。宿主程序根据 c 指向的查询结果关系集合，使用 open, fetch, close 依次获取结果关系中的各元组

open c: the SQL query is evaluated, and the cursor is set to point to the first tuple of the result relation

fetch c: the tuple pointed by the cursor is retrieved and fetched into some shared variables, and then the cursor is updated to point to the next tuple of the result

close c: the result relation is deleted by DBMS

4.4.2 Cursor in Embedded SQL


Usage of cursor in embedded SQL

declare cursor – open – fetch - close

DBS

…results

SQL query

application program:

open fetch close

cursorworking area

4.4.2 Cursor in Embedded SQL (cont.)

Fig. 4.0.5 Cursor in Embedded SQL


E.g.2 From within C language, find the names and cities of customers with more than the variable amount ( input from screen by users) dollars in some account


the C program is as follows

EXEC SQL BEGIN DECLARE SECTION int amount; char cn; char cc;

EXEC SQL END DECLARE SECTION amount := input-from-screen-by-users EXEC SQL declare c cursor for select customer-name, customer-city

from depositor, customer, accountwhere depositor.customer-name = customer.customer-name and depositor account-number = account.account- number and account.balance> :amount

END-EXEC EXEC SQL open c END-EXEC EXEC SQL fetch c into :cn, :cc END-EXEC EXEC SQL close c END-EXEC

shared variable


Notes the open statement causes the query to be evaluated

evaluating query specified by c, applying :amount to the query

the query result is stored in a temporal relation the fetch statement causes the values of one tuple in the

query result to be placed on host language variables :cn and :cc

:cn corresponds to customer-name, :cc corresponds to customer-city

the close statement causes the DBS to delete the temporary relation that holds the result of the query



A variable called SQLSTATE in the SQL communication area (SQLCA) gets set to ‘02000’ to indicate no more data is available

Tuples fetched can be updated by cursor by declaring that the cursor is for update E.g.

declare c cursor for select * from account where branch-name = ‘Perryridge’ for update



To update tuple at the current location of cursor

update account set balance = balance + 100 where current of c



§4.5 Dynamic SQL&ODBC/JDBC

Dynamic SQL allows programs to construct and submit SQL queries at run time.

Example of the use of dynamic SQL from within a C program.

char * sqlprog = “update account set balance = balance * 1.05

where account-number = ?”EXEC SQL prepare dynprog from :sqlprog;char account [10] = “A-101”;EXEC SQL execute dynprog using :account;

The dynamic SQL program contains a ?, which is a place holder for a value that is provided when the SQL program is executed.


ODBC acronym for Open DataBase Connectivity in the Microsoft WOSA structure, an interface providing a

common language for windows applications to gain access a database on networks

WOSA acronym for Windows Open System Architecture a set of application programming interfaces from Microsoft

that is intended to enable Windows applications form different vendors to communicate with each other, such as over a network

the interfaces within the WOSA standard include

4.5.1 ODBC (cont.)


Open DataBase Connectivity, ODBC the Message Application Programming Interface, MAPI the Telephony Application Programming Interface,

TAPI Windows Socket, Winsock Micro Remote Procedure Calls, RPC

The functions of ODBC standard for application programs to communicate with a

database server. application program interface (API) to

open a connection with a database send queries and updates get back results

4.5.1 ODBC (cont.)


Architecture of ODBC refer to Fig. 4.0.6

For more details about ODBC, refer to SQL Server —4—ODBC

4.5.1 ODBC (cont.)

Database application programs

ODBC API

ODBC manager

ODBC driver manager

SQL Serverdriver

Oracledriver

Sybasedriver

other DBdriver

SQLServer

Oracle Sybase other

DBMS

Data SourceName

ApplicationLevel

ODBCLevel

Data SourceLevel

Fig.4.0.6 ODBC Architecture


JDBC acronym for Java DataBase Connectivity a Java API for communicating with database systems

supporting SQL JDBC supports a variety of features for querying and updating

data, and for retrieving query results JDBC also supports metadata retrieval, such as querying about

relations present in the database and the names and types of relation attributes

Model for communicating with the database open a connection

4.5.2 JDBC


create a “statement” object execute queries using the Statement object to send queries and

fetch results Exception mechanism to handle errors

Transactions in JDBC as with ODBC, each statement gets committed automatically

in JDBC to turn off auto commit use

conn.setAutoCommit(false); to commit or abort transactions use

conn.commit() or conn.rollback() to turn auto commit on again, use

conn.setAutoCommit(true);

4.5.2 JDBC (cont.)


SQL provides a module language permits definition of procedures in SQL, with if-then-else

statements, for and while loops, etc. more in Chapter 9

Stored Procedures ( 存储过程 ) can store procedures in the database then execute them using the call statement permit external applications to operate on the database

without knowing about internal details These features are covered in Chapter 9 (Object Relational

Databases)

§4.6 Functions and Procedures


Functions and Procedures (cont.)

SQL:1999 supports functions and procedures functions/procedures can be written in SQL itself, or in an

external programming language functions are particularly useful with specialized data types such

as images and geometric objects e.g.: functions to check if polygons overlap, or to compare

images for similarity some database systems support table-valued functions, which

can return a relation as a result SQL:1999 also supports a rich set of imperative constructs,

including loops, if-then-else, assignment

Many databases have proprietary procedural extensions to SQL that differ from SQL:1999


Define a function that, given the name of a customer, returns the count of the number of accounts owned by the customer.

create function account_count (customer_name varchar(20)) returns integer begin declare a_count integer; select count (* ) into a_count from depositor where depositor.customer_name = customer_name return a_count; end



Find the name and address of each customer that has more than one account.

select customer_name, customer_street, customer_cityfrom customerwhere account_count (customer_name ) > 1



Assuming a foreign key of table r2 references the primary key attributes K of the referenced table r1

An example, as shown in Fig.6.0.2 r1 (R1) : branch (branch-name, branch-city, assets )

r2 (R2) : account (account-number, branch-name, balance) : branch-name t1 = (New-York-branch , New York , $2000) in r1

t2 = (201#, New-York-branch, $500) in r2

Appendix A Database Modification


When the DB is modified by Insert, Delete, and Update, the tests for must be made in order to preserve the following referential integrity constraint:

(r2) K (r1)


Appendix A Database Modification (cont.)


Insert vs. referential integrity if a tuple t2 is inserted into r2 (e.g. account), the system must

ensure that there is a tuple t1 in r1 (e.g. branch) such that

t1[K1] = t2[], i.e. t2 [] K1 (r1)

e.g. insert t2 = (303#, Brooklyn-branch, $400) into account, t1= (Brooklyn-branch , * , *) exists in branch ?

e.g. t2 []=“Brooklyn-branch” branch-name (branch)

/*新插入的 account的开户行是否已在 branch中存在？



Delete vs. referential integrity if a tuple t1 is deleted from r1 (e.g. branch), the system must

compute the set of tuples in r2 (e.g. account) that reference t1:

= t1[K1] (r2) e.g. delete t1=(New-York , New York, $5000) from

branch,

= t1[K1] (r2)

= branch-name = New-York (account)

= {t | t = ( *, New-York, * ) }

/* 所有在被删除的 New-York 支行中的 account 元组



if this set is not empty either the delete command is rejected as an error, or

/* 不允许 delete t1=(New-York, New York, $5000) from branch

the tuples in r2 that reference t1 must themselves be deleted (cascading deletions are possible)

/* 所有在被删除的 New-York 支行中的 account 元组需要同时被删除（级联删除）



Update vs. referential integrity. Two cases as following Case1. If a tuple t2 is updated in relation r2 (e.g. account), and

the update modifies values for foreign key (e.g. branch-name), then a test similar to the insert case is made let t2’ denote the new value of tuple t2, the system must

ensure that

t2’[] K1(r1) e.g. if update t2= (201#, New-York-branch, $500) into

t2’ = (80#, Austin-branch, $500) in account, is

t2’[] = Austin-branch branch-name(branch) ?

/* 判断新改成的支行 Los-Angles-branch 是否存在？



Case2. if a tuple t1 in r1 (e.g. branch) is updated, and the update modifies values for the primary key K1 of r1 (e.g. branch-name), then a test similar to the delete case is made e.g. t1=(New-York , New York, $5000) is updated into

t1=(N-YY, New York, $5000)

the system must compute = t1[K1] (r2) using the old value of t1 (the value before the update is applied)

branch-name = New-York(account) if this set is not empty

/* 在原来的 New-York 支行中有 account 元组 , e.g. (201#, New-York, $500), (203#, New-York, $1000)



the update may be rejected as an error, or

/* 不允许对 branch 进行修改，即不允许将 t1=(New-York , New York, $5000) 修改为 t1=(N-YY , New York, $5000)

the update may be cascaded in a manner similar to delete

/* 将所有 account 元组， e.g. (201#, New-York, $500) 修改为 (201#, N-YY, $500)



In SQL, primary and foreign keys can be specified as part of the create table statement the primary key clause lists attributes that comprise the

primary key the foreign key-reference clause lists the attributes that

comprise the foreign key and the name of the relation referenced by the foreign key



E.g.1 Fig.6.2

create table depositor (customer-name char(20), account-number char(10), primary key (customer-name, account-number), foreign key (account-number) references account, foreign key (customer-name) references customer)

When a referential integrity is violated due to a delete or update action on the referenced relation, in stead of rejecting the action(e.g. delete, update) causing the violation, the foreign key-reference clause can specify the remedying steps to change the tuples in referencing relation to restore the constraints



E.g. 2 create table account

( . . .foreign key(branch-name) references branch

on delete cascadeon update cascade

. . . ) account is the the referencing relation, branch is the

referenced relation the on delete cascade clause defines if a delete of a tuple in

the referenced branch results in referential-integrity constraint violation, the delete cascade to the referencing account should delete all the tuple that refers to the branch that was deleted



the on update cascade clause specifies that if an update to branch-name in the referenced tuple in branch violates the referential-integrity constraint, the system should also update the field branch-name in the referencing tuples in account to the new values

Besides cascading, if the constraints is violated, the referencing field can be set to null or predefined default

values by clauses on delete set null , or on delete set default


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PART 2 RELATIONAL DATABASES. Chapter 4 Advanced SQL