Ch4

Database System Concepts, 6th
Ed.
©Silberschatz, Korth and Sudarshan
See www.db-book.com for conditions on re-use
Chapter 4: Intermediate SQLChapter 4: Intermediate SQL

©Silberschatz, Korth and Sudarshan4.2Database System Concepts - 6th
Edition
Chapter 4: Intermediate SQLChapter 4: Intermediate SQL
Join Expressions
Views
Transactions
Integrity Constraints
SQL Data Types and Schemas
Authorization

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Joined RelationsJoined Relations
Join operations take two relations and return as a result
another relation.
A join operation is a Cartesian product which requires that
tuples in the two relations match (under some condition).
It also specifies the attributes that are present in the result
of the join
The join operations are typically used as subquery
expressions in the from clause

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Join operations – ExampleJoin operations – Example
Relation course
Relation prereq
Observe that
prereq information is missing for CS-315 and
course information is missing for CS-437

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Outer JoinOuter Join
An extension of the join operation that avoids loss of
information.
Computes the join and then adds tuples form one relation
that does not match tuples in the other relation to the result
of the join.
Uses null values.

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Left Outer JoinLeft Outer Join
course natural left outer join prereq

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Right Outer JoinRight Outer Join
course natural right outer join prereq

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Joined RelationsJoined Relations
Join operations take two relations and return as a result
another relation.
These additional operations are typically used as subquery
expressions in the from clause
Join condition – defines which tuples in the two relations
match, and what attributes are present in the result of the join.
Join type – defines how tuples in each relation that do not
match any tuple in the other relation (based on the join
condition) are treated.

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Full Outer JoinFull Outer Join
course natural full outer join
prereq

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Joined Relations – ExamplesJoined Relations – Examples
course inner join prereq on
course.course_id = prereq.course_id
What is the difference between the above, and a natural join?
course left outer join prereq on
course.course_id = prereq.course_id

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Joined Relations – ExamplesJoined Relations – Examples
course natural right outer join prereq
course full outer join prereq using (course_id)

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ViewsViews
In some cases, it is not desirable for all users to see the entire
logical model (that is, all the actual relations stored in the
database.)
Consider a person who needs to know an instructors name
and department, but not the salary. This person should see a
relation described, in SQL, by
select ID, name, dept_name
from instructor
A view provides a mechanism to hide certain data from the
view of certain users.
Any relation that is not of the conceptual model but is made
visible to a user as a “virtual relation” is called a view.

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View DefinitionView Definition
A view is defined using the create view statement which has
the form
create view v as < query expression >
where <query expression> is any legal SQL expression. The
view name is represented by v.
Once a view is defined, the view name can be used to refer to
the virtual relation that the view generates.
View definition is not the same as creating a new relation by
evaluating the query expression
Rather, a view definition causes the saving of an expression;
the expression is substituted into queries using the view.

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Example ViewsExample Views
A view of instructors without their salary
create view faculty as
select ID, name, dept_name
from instructor
Find all instructors in the Biology department
select name
from faculty
where dept_name = ‘Biology’
Create a view of department salary totals
create view departments_total_salary(dept_name, total_salary)
as
select dept_name, sum (salary)
from instructor
group by dept_name;

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Views Defined Using Other ViewsViews Defined Using Other Views
create view physics_fall_2009 as
select course.course_id, sec_id, building, room_number
from course, section
where course.course_id = section.course_id
and course.dept_name = ’Physics’
and section.semester = ’Fall’
and section.year = ’2009’;
create view physics_fall_2009_watson as
select course_id, room_number
from physics_fall_2009
where building= ’Watson’;

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View ExpansionView Expansion
Expand use of a view in a query/another view
create view physics_fall_2009_watson as
(select course_id, room_number
from (select course.course_id, building, room_number
from course, section
where course.course_id = section.course_id
and course.dept_name = ’Physics’
and section.semester = ’Fall’
and section.year = ’2009’)
where building= ’Watson’;

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Views Defined Using Other ViewsViews Defined Using Other Views
One view may be used in the expression defining another view
A view relation v1 is said to depend directly on a view relation v2
if v2 is used in the expression defining v1
A view relation v1 is said to depend on view relation v2 if either
v1 depends directly to v2 or there is a path of dependencies
from v1 to v2
A view relation v is said to be recursive if it depends on itself.

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View ExpansionView Expansion
A way to define the meaning of views defined in terms of other
views.
Let view v1 be defined by an expression e1 that may itself
contain uses of view relations.
View expansion of an expression repeats the following
replacement step:
repeat
Find any view relation vi in e1
Replace the view relation vi by the expression defining vi
until no more view relations are present in e1
As long as the view definitions are not recursive, this loop will
terminate

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Update of a ViewUpdate of a View
Add a new tuple to faculty view which we defined earlier
insert into faculty values (’30765’, ’Green’, ’Music’);
This insertion must be represented by the insertion of the tuple
(’30765’, ’Green’, ’Music’, null)
into the instructor relation

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Some Updates cannot be TranslatedSome Updates cannot be Translated
UniquelyUniquely
create view instructor_info as
select ID, name, building
from instructor, department
where instructor.dept_name= department.dept_name;
insert into instructor_info values (’69987’, ’White’, ’Taylor’);
 which department, if multiple departments in Taylor?
 what if no department is in Taylor?
Most SQL implementations allow updates only on simple views
The from clause has only one database relation.
The select clause contains only attribute names of the
relation, and does not have any expressions, aggregates, or
distinct specification.
Any attribute not listed in the select clause can be set to null
The query does not have a group by or having clause.

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And Some Not at AllAnd Some Not at All
create view history_instructors as
select *
from instructor
where dept_name= ’History’;
What happens if we insert (’25566’, ’Brown’, ’Biology’, 100000)
into history_instructors?

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Materialized Views
Materializing a view: create a physical table containing all the
tuples in the result of the query defining the view
If relations used in the query are updated, the materialized view result
becomes out of date
Need to maintain the view, by updating the view whenever the
underlying relations are updated.

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Transactions
Unit of work
Atomic transaction
either fully executed or rolled back as if it never occurred
Isolation from concurrent transactions
Transactions begin implicitly
Ended by commit work or rollback work
But default on most databases: each SQL statement commits
automatically
Can turn off auto commit for a session (e.g. using API)
In SQL:1999, can use: begin atomic …. end
 Not supported on most databases

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Integrity ConstraintsIntegrity 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.
A checking account must have a balance greater than
$10,000.00
A salary of a bank employee must be at least $4.00 an
hour
A customer must have a (non-null) phone number

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Integrity Constraints on a Single RelationIntegrity Constraints on a Single Relation
not null
primary key
unique
check (P), where P is a predicate

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Not Null and Unique ConstraintsNot Null and Unique Constraints
not null
Declare name and budget to be not null
name varchar(20) not null
budget numeric(12,2) not null
unique ( A1, A2, …, Am)
The unique specification states that the attributes A1, A2, …
Am
form a candidate key.
Candidate keys are permitted to be null (in contrast to primary
keys).

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The check clauseThe check clause
check (P)
where P is a predicate
Example: ensure that semester is one of fall, winter, spring
or summer:
create table section (
course_id varchar (8),
sec_id varchar (8),
semester varchar (6),
year numeric (4,0),
building varchar (15),
room_number varchar (7),
time slot id varchar (4),
primary key (course_id, sec_id, semester, year),
check (semester in (’Fall’, ’Winter’, ’Spring’, ’Summer’))
);

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Referential IntegrityReferential Integrity
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.
Example: If “Biology” is a department name appearing in
one of the tuples in the instructor relation, then there exists
a tuple in the department relation for “Biology”.
Let A be a set of attributes. Let R and S be two relations that
contain attributes A and where A is the primary key of S. A is
said to be a foreign key of R if for any values of A
appearing in R these values also appear in S.

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Cascading Actions in Referential IntegrityCascading Actions in Referential Integrity
create table course (
course_id char(5) primary key,
title varchar(20),
dept_name varchar(20) references department
)
create table course (
…
dept_name varchar(20),
foreign key (dept_name) references department
on delete cascade
on update cascade,
. . .
)
alternative actions to cascade: set null, set default

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Integrity Constraint Violation DuringIntegrity Constraint Violation During
TransactionsTransactions
E.g.
create table person (
ID char(10),
name char(40),
mother char(10),
father char(10),
primary key ID,
foreign key father references person,
foreign key mother references person)
How to insert a tuple without causing constraint violation ?
insert father and mother of a person before inserting person
OR, set father and mother to null initially, update after
inserting all persons (not possible if father and mother
attributes declared to be not null)
OR defer constraint checking (next slide)

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Complex Check ClausesComplex Check Clauses
check (time_slot_id in (select time_slot_id from time_slot))
why not use a foreign key here?
Every section has at least one instructor teaching the section.
how to write this?
Unfortunately: subquery in check clause not supported by
pretty much any database
Alternative: triggers (later)
create assertion <assertion-name> check <predicate>;
Also not supported by anyone

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Built-in Data Types in SQLBuilt-in Data Types in SQL
date: Dates, containing a (4 digit) year, month and date
Example: date ‘2005-7-27’
time: Time of day, in hours, minutes and seconds.
Example: time ‘09:00:30’ time ‘09:00:30.75’
timestamp: date plus time of day
Example: timestamp ‘2005-7-27 09:00:30.75’
interval: period of time
Example: interval ‘1’ day
Subtracting a date/time/timestamp value from another gives
an interval value
Interval values can be added to date/time/timestamp values

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Index CreationIndex Creation
create table student
(ID varchar (5),
name varchar (20) not null,
dept_name varchar (20),
tot_cred numeric (3,0) default 0,
primary key (ID))
create index studentID_index on student(ID)
Indices are data structures used to speed up access to records
with specified values for index attributes
e.g. select *
from student
where ID = ‘12345’
can be executed by using the index to find the required record,
without looking at all records of student
More on indices in Chapter 11

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User-Defined TypesUser-Defined Types
create type construct in SQL creates user-defined type
create type Dollars as numeric (12,2) final
create table department
(dept_name varchar (20),
building varchar (15),
budget Dollars);

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DomainsDomains
create domain construct in SQL-92 creates user-defined
domain types
create domain person_name char(20) not null
Types and domains are similar. Domains can have
constraints, such as not null, specified on them.
create domain degree_level varchar(10)
constraint degree_level_test
check (value in (’Bachelors’, ’Masters’, ’Doctorate’));

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Large-Object TypesLarge-Object Types
Large objects (photos, videos, CAD files, etc.) are stored as a
large object:
blob: binary large object -- 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 -- 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.

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AuthorizationAuthorization
Forms of authorization on parts of the database:
Read - allows reading, but not modification of data.
Insert - allows insertion of new data, but not modification of
existing data.
Update - allows modification, but not deletion of data.
Delete - allows deletion of data.
Forms of authorization to modify the database schema
Index - allows creation and deletion of indices.
Resources - allows creation of new relations.
Alteration - allows addition or deletion of attributes in a relation.
Drop - allows deletion of relations.

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Authorization Specification in SQLAuthorization 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 later)
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).

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Privileges in SQLPrivileges 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 instructor relation:
grant select on instructor 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

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Revoking Authorization in SQLRevoking 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.
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.

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Roles
create role instructor;
grant instructor to Amit;
Privileges can be granted to roles:
grant select on takes to instructor;
Roles can be granted to users, as well as to other roles
create role teaching_assistant
grant teaching_assistant to instructor;
 Instructor inherits all privileges of teaching_assistant
Chain of roles
create role dean;
grant instructor to dean;
grant dean to Satoshi;

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Authorization on ViewsAuthorization on Views
create view geo_instructor as
(select *
from instructor
where dept_name = ’Geology’);
grant select on geo_instructor to geo_staff
Suppose that a geo_staff member issues
select *
from geo_instructor;
What if
geo_staff does not have permissions on instructor?
creator of view did not have some permissions on
instructor?

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Other Authorization FeaturesOther Authorization Features
references privilege to create foreign key
grant reference (dept_name) on department to
Mariano;
why is this required?
transfer of privileges
grant select on department to Amit with grant option;
revoke select on department from Amit, Satoshi
cascade;
revoke select on department from Amit, Satoshi
restrict;
Etc. read Section 4.6 for more details we have omitted here.

Database System Concepts, 6th
Ed.
©Silberschatz, Korth and Sudarshan
See www.db-book.com for conditions on re-use
End of Chapter 4End of Chapter 4

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Figure 4.01Figure 4.01

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Taylor

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