Database management system chapter seven

Chapter 7
SQL – Data Definition
Pearson Education © 2014

Chapter 7 - Objectives
Data types supported by SQL standard.
Purpose of integrity enhancement feature of
SQL.
How to define integrity constraints using SQL.
How to use the integrity enhancement feature
in the CREATE and ALTER TABLE statements.
Pearson Education © 2014 2

Chapter 7 - Objectives
Purpose of views.
How to create and delete views using SQL.
How the DBMS performs operations on
views.
Under what conditions views are updatable.
Advantages and disadvantages of views.
How the ISO transaction model works.
How to use the GRANT and REVOKE
statements as a level of security.

Data Definition
SQL DDL allows database objects such as
schemas, domains, tables, views, and indexes
to be created and destroyed.
Main SQL DDL statements are:
CREATE SCHEMA DROP SCHEMA
CREATE/ALTER DOMAIN DROP DOMAIN
CREATE/ALTER TABLE DROP TABLE
CREATE VIEWDROP VIEW
Many DBMSs also provide:
CREATE INDEX DROP INDEX

Data Definition
• Relations and other database objects exist in
an environment.
• Each environment contains one or more
catalogs, and each catalog consists of set of
schemas.
• Schema is named collection of related
database objects.
• Objects in a schema can be tables, views,
domains, assertions, collations, translations,
and character sets. All have same owner.

CREATE SCHEMA
CREATE SCHEMA [Name |
AUTHORIZATION CreatorId ]
DROP SCHEMA Name [RESTRICT | CASCADE ]
• With RESTRICT (default), schema must be
empty or operation fails.
• With CASCADE, operation cascades to drop
all objects associated with schema in order
defined above. If any of these operations
fail, DROP SCHEMA fails.

CREATE TABLE
CREATE TABLE TableName (
{(colName dataType [NOT NULL] [UNIQUE]
[DEFAULT defaultOption]
[CHECK searchCondition] [,...]}
[PRIMARY KEY (listOfColumns),]
{[UNIQUE (listOfColumns),] […,]}
{[FOREIGN KEY (listOfFKColumns)
REFERENCES ParentTableName [(listOfCKColumns)],
[ON UPDATE referentialAction]
[ON DELETE referentialAction ]] [,…]}
{[CHECK (searchCondition)] [,…] });

CREATE TABLE
• Creates a table with one or more columns of
the specified dataType.
• With NOT NULL, system rejects any attempt
to insert a null in the column.
• Can specify a DEFAULT value for the column.
• Primary keys should always be specified as
NOT NULL.
• FOREIGN KEY clause specifies FK along with
the referential action.

Example 7.1 - CREATE TABLE
CREATE TABLE PropertyForRent (
propertyNo VARCHAR(5),
rooms SMALLINT,
rent DECIMAL (6,2),
ownerNo VARCHAR(5),
staffNo VARCHAR(5),
branchNo CHAR(4),
PRIMARY KEY (propertyNo),
FOREIGN KEY (staffNo) REFERENCES Staff);

ISO SQL Data Types

CHAR or VARCHAR
• Data to store ‘ABCD’
– CHAR(4) 4 bytes
– VARCHAR(4) 5-6 bytes (1-2 bytes eos)
– CHAR (200) 200 bytes
– VARCHAR(200) 5-6 bytes
• So, use CHAR for short, fixed length items (e.g.,
SSN)
– Get benefits of data type checking on insert
• If input string is too long, get error message
(STRICT SQL enabled) or truncation (STRICT not
enabled)

ENUMERATIONS
• In MySQL, (if invalid insert, ‘’ empty string is
inserted instead)
CREATE TABLE Beverages (
Name VARCHAR (20)
Price DECIMAL(4,2)
Size ENUM (‘venti’, ‘grande’, ‘tall’)
);
• In Oracle
–CREATE TABLE Beverages (
•Name VARCHAR (20)
•Price DECIMAL(4,2)
•Size VARCHAR (6) CHECK Size IN (‘venti’, ‘grande’, ‘tall’)
•);

Integrity Enhancement Feature
• Consider five types of integrity constraints:
– required data
– domain constraints
– entity integrity
– referential integrity
– general constraints.

DECIMAL/NUMERIC
• DECIMAL (precision, scale)
– DECIMAL (5,2)
• 123 -> 123.00
• ~same as NUMERIC
• Too many digits prior to ‘.’
– Throws an error (e.g., 1234)
• Too many digits after ‘.’
– Truncates (e.g., 123.456 -> 123.45)

Required Data
position VARCHAR(10) NOT NULL
Domain Constraints
(a)CHECK
student_type CHAR NOT NULL
CHECK (student_type IN (‘U’,
‘G’))

(b) CREATE DOMAIN
CREATE DOMAIN DomainName [AS] dataType
[DEFAULT defaultOption]
[CHECK (searchCondition)]
For example:
CREATE DOMAIN StudentType AS CHAR
CHECK (VALUE IN (‘U’, ‘G’));
In CREATE TABLE Student:
student_type StudentType NOT NULL

• searchCondition can involve a table lookup:
CREATE DOMAIN BranchNo AS CHAR(4)
CHECK (VALUE IN (SELECT branchNo
FROM Branch));
• Domains can be removed using DROP
DOMAIN:
DROP DOMAIN DomainName [RESTRICT|
CASCADE];
// RESTRICT: only if empty; CASCADE: drop column

IEF - Entity Integrity
• Primary key of a table must contain a unique,
non-null value for each row.
• ISO standard supports FOREIGN KEY clause in
CREATE and ALTER TABLE statements:
PRIMARY KEY(staffNo)
PRIMARY KEY(clientNo, propertyNo)
• Can only have one PRIMARY KEY clause per
table. Can still ensure uniqueness for
alternate keys using UNIQUE:
UNIQUE(telNo)

IEF - Referential Integrity
• FK is column or set of columns that links each
row in child table containing foreign FK to row
of parent table containing matching PK.
• Referential integrity means that, if FK contains
a value, that value must refer to existing row
in parent table.
• ISO standard supports definition of FKs with
FOREIGN KEY clause in CREATE and ALTER
TABLE:
FOREIGN KEY(branchNo) REFERENCES Branch

• Any INSERT/UPDATE attempting to create FK
value in child table without matching CK value
in parent is rejected.
• Action taken when update/delete a CK value
in parent table with matching rows in child is
dependent on referential action specified
using ON UPDATE and ON DELETE subclauses:
– CASCADE
– SET NULL
– SET DEFAULT
– NO ACTION Pearson Education © 2014 20

CASCADE: Delete row from parent and delete
matching rows in child, and so on in cascading
manner.
SET NULL: Delete row from parent and set FK
column(s) in child to NULL.
SET DEFAULT: Delete row from parent and set
each component of FK in child to specified
default. Only valid if DEFAULT specified for FK
columns.
NO ACTION: Reject delete from parent. Default.

FOREIGN KEY (staffNo) REFERENCES Staff
ON DELETE SET NULL
FOREIGN KEY (ownerNo) REFERENCES Owner
ON UPDATE CASCADE

IEF - General Constraints
• Could use CHECK/UNIQUE in CREATE and
ALTER TABLE.
• Similar to the CHECK clause, also have:
CREATE ASSERTION AssertionName
CHECK (searchCondition)

IEF - General Constraints
CREATE ASSERTION StaffNotHandlingTooMuch
CHECK (NOT EXISTS (SELECT staffNo
FROM PropertyForRent
GROUP BY staffNo
HAVING COUNT(*) >
100));

CREATE DOMAIN OwnerNumber AS VARCHAR(5)
CHECK (VALUE IN (SELECT ownerNo FROM PrivateOwner));
CREATE DOMAIN StaffNumber AS VARCHAR(5)
CHECK (VALUE IN (SELECT staffNo FROM Staff));
CREATE DOMAIN PNumber AS VARCHAR(5);
CREATE DOMAIN PRooms AS SMALLINT;
CHECK(VALUE BETWEEN 1 AND 15);
CREATE DOMAIN PRent AS DECIMAL(6,2)
CHECK(VALUE BETWEEN 0 AND 9999.99);

CREATE TABLE PropertyForRent (
propertyNo PNumber NOT NULL, ….
rooms PRoomsNOT NULL DEFAULT 4,
rent PRentNOT NULL, DEFAULT 600,
ownerNo OwnerNumber NOT NULL,
staffNo StaffNumber
Constraint StaffNotHandlingTooMuch ….
branchNo BranchNumber NOT NULL,
PRIMARY KEY (propertyNo),
FOREIGN KEY (staffNo) REFERENCES Staff
ON DELETE SET NULL ON UPDATE CASCADE ….);

ALTER TABLE
• Add a new column to a table.
• Drop a column from a table.
• Add a new table constraint.
• Drop a table constraint.
• Set a default for a column.
• Drop a default for a column.

Example 7.2(a) - ALTER TABLE
Change Staff table by removing default of
‘Assistant’ for position column and setting
default for sex column to female (‘F’).
ALTER TABLE Staff
ALTER position DROP DEFAULT;
ALTER TABLE Staff
ALTER gender SET DEFAULT ‘F’;

Example 7.2(b) - ALTER TABLE
Remove constraint from PropertyForRent
that staff are not allowed to handle more
than 100 properties at a time. Add new
column to Client table.
ALTER TABLE PropertyForRent
DROP CONSTRAINT StaffNotHandlingTooMuch;
ALTER TABLE Client
ADD prefNoRooms PRooms;

DROP TABLE
DROP TABLE TableName [RESTRICT | CASCADE]
e.g. DROP TABLE PropertyForRent;
• Removes named table and all rows within it.
• With RESTRICT, if any other objects depend for
their existence on continued existence of this
table, SQL does not allow request.
• With CASCADE, SQL drops all dependent
objects (and objects dependent on these
objects).

Views
View
Dynamic result of one or more relational
operations operating on base relations to
produce another relation.
• Virtual relation that does not necessarily
actually exist in the database but is produced
upon request, at time of request.

Views
• Contents of a view are defined as a query on
one or more base relations.
• With view resolution, any operations on view
are automatically translated into operations
on relations from which it is derived.
• With view materialization, the view is stored
as a temporary table, which is maintained as
the underlying base tables are updated.

SQL - CREATE VIEW
CREATE VIEW ViewName [ (newColumnName [,...]) ]
AS subselect
[WITH [CASCADED | LOCAL] CHECK OPTION]
• Can assign a name to each column in view.
• If list of column names is specified, it must
have same number of items as number of
columns produced by subselect.
• If omitted, each column takes name of
corresponding column in subselect.

SQL - CREATE VIEW
• List must be specified if there is any ambiguity
in a column name.
• The subselect is known as the defining query.
• WITH CHECK OPTION ensures that if a row
fails to satisfy WHERE clause of defining
query, it is not added to underlying base
table.
• Need SELECT privilege on all tables referenced
in subselect and USAGE privilege on any
domains used in referenced columns.

Example 7.3 - Create Horizontal View
Create view so that manager at branch B003 can
only see details for staff who work in his or her
office.
“Horizontal” i.e., a subset of the rows
CREATE VIEW Manager3Staff
AS SELECT *
FROM Staff
WHERE branchNo = ‘B003’;

Example 7.4 - Create Vertical View
Create view of staff details at branch B003
excluding salaries.
Subset of columns (also example of dependent
View);
CREATE VIEW Staff3Staff
AS SELECT staffNo, fName, lName, position, sex
FROM Manager3Staff;
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SQL - DROP VIEW
DROP VIEW ViewName [RESTRICT | CASCADE]
• Causes definition of view to be deleted from
database.
• For example:
DROP VIEW Manager3Staff RESTRICT;
- should not be allowed due to Staff3Staff;
DROP VIEW Manager3Staff; (Default: CASCADE?]
DROP VIEW Manager3Staff CASCADE;
- will also drop Staff3Staff;

SQL - DROP VIEW
• With CASCADE, all related dependent objects
are deleted; i.e. any views defined on view
being dropped.
• With RESTRICT (default), if any other objects
depend for their existence on continued
existence of view being dropped, command is
rejected.

SQL - DROP VIEW
DROP VIEW Manager3Staff;
- should drop Manager3Staff, leave Staff3Staff
DROP VIEW Manager3Staff RESTRICT;
- should not be allowed due to Staff3Staff;
DROP VIEW Manager3Staff CASCADE;
- will also drop Staff3Staff;
NOTE: In mysql, CASCADE/RESTRICT are parsed and
ignored:
https://dev.mysql.com/doc/refman/8.0/en/drop-view.html

Example 7.5 - Grouped and Joined
Views
Create view of staff who manage properties
for rent, including branch number they work
at, staff number, and number of properties
they manage.
CREATE VIEW StaffPropCnt (branchNo, staffNo, cnt)
AS SELECT s.branchNo, s.staffNo, COUNT(*)
FROM Staff s, PropertyForRent p
WHERE s.staffNo = p.staffNo
GROUP BY s.branchNo, s.staffNo;

Example 7.3 - Grouped and Joined
Views

View Updatability
• All updates to base table reflected in all
views that encompass base table.
• Similarly, may expect that if view is updated
then base table(s) will reflect change.

View Updatability
• However, consider again view StaffPropCnt.
• If we tried to insert record showing that at
branch B003, SG5 manages 2 properties:
INSERT INTO StaffPropCnt
VALUES (‘B003’, ‘SG5’, 2);
• Have to insert 2 records into
PropertyForRent showing which properties
SG5 manages. However, do not know which
properties they are; i.e. do not know primary
keys! So, this is not allowed.

Updatable View
For view to be updatable, DBMS must be
able to trace any row or column back to its
row or column in the source table.

Advantages of Views
• Data independence
• Currency
• Improved security
• Reduced complexity
• Convenience
• Customization
• Data integrity

Disadvantages of Views
• Update restriction
• Structure restriction
• Performance

View Materialization
• View resolution mechanism may be slow,
particularly if view is accessed frequently.
• View materialization stores view as
temporary table when view is first queried.
• Thereafter, queries based on materialized
view can be faster than recomputing view
each time.
• Difficulty is maintaining the currency of view
while base tables(s) are being updated.

Access Control - Authorization Identifiers and
Ownership
• Authorization identifier is normal SQL
identifier used to establish identity of a user.
Usually has an associated password.
• Used to determine which objects user may
reference and what operations may be
performed on those objects.
• Each object created in SQL has an owner, as
defined in AUTHORIZATION clause of schema
to which object belongs.
• Owner is only person who may know about it.

Privileges
• Actions user permitted to carry out on given
base table or view:
SELECT Retrieve data from a table.
INSERT Insert new rows into a table.
UPDATE Modify rows of data in a table.
DELETE Delete rows of data from a table.
REFERENCES Reference columns of named table
in integrity constraints.
USAGE Use domains, collations, character sets,
and translations.

Privileges
• Can restrict INSERT/UPDATE/REFERENCES to
named columns.
• Owner of table must grant other users the
necessary privileges using GRANT statement.
• To create view, user must have SELECT
privilege on all tables that make up view and
REFERENCES privilege on the named columns.

GRANT
GRANT {PrivilegeList | ALL PRIVILEGES}
ON ObjectName
TO {AuthorizationIdList | PUBLIC}
[WITH GRANT OPTION]
• PrivilegeList consists of one or more of above
privileges separated by commas.
• ALL PRIVILEGES grants all privileges to a user.

GRANT
• PUBLIC allows access to be granted to all
present and future authorized users.
• ObjectName can be a base table, view,
domain, character set, collation or
translation.
• WITH GRANT OPTION allows privileges to be
passed on.

Example 7.7/8 - GRANT
Give Manager full privileges to Staff table.
GRANT ALL PRIVILEGES
ON Staff
TO Manager WITH GRANT OPTION;
Give users Personnel and Director SELECT and
UPDATE on column salary of Staff.
GRANT SELECT, UPDATE (salary)
ON Staff
TO Personnel, Director;

Example 7.9 - GRANT Specific Privileges to
PUBLIC
Give all users SELECT on Branch table.
GRANT SELECT
ON Branch
TO PUBLIC;

REVOKE
• REVOKE takes away privileges granted with
GRANT.
REVOKE [GRANT OPTION FOR]
{PrivilegeList | ALL PRIVILEGES}
ON ObjectName
FROM {AuthorizationIdList | PUBLIC}
[RESTRICT | CASCADE]
• ALL PRIVILEGES refers to all privileges granted
to a user by user revoking privileges.

Example 7.10/11 - REVOKE Specific
Privileges
Revoke privilege SELECT on Branch table from
all users.
REVOKE SELECT
ON Branch
FROM PUBLIC;
Revoke all privileges given to Director on Staff
table.
REVOKE ALL PRIVILEGES
ON Staff
FROM Director;

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