Download Rule 3: Systematic Treatment of NULL values

Q-1 PL/SQL data types
PL/SQL variables, constants and parameters must have a valid data types which specifies a storage format,
constraints, and valid range of values.
Numeric Data types & Subtypes
Data type
Range
Dec(p,s)
Upto 38 digits
Decimal(p,s)
Upto 38 digits
Number(p,s)
Upto 38 digits
Numeric(p,s)
Upto 38 digits
Integer
Int
Real
Float
Upto 38 digits
Upto 38 digits
Upto 18 digits
Upto 38 digits
Binary_float
Single precision IEEE 754 format
floating point number
double precision IEEE 754 format
floating point number
Binary_double
Character Data types & Subtypes
Data type
Range
Char
Upto 32767 bytes
Varchar2
Upto 32767 bytes
Raw
Long Raw
Nchar
Upto 32767 bytes
Upto 2 gb
Upto 32767 bytes
Nvarchar2
Upto 32767 bytes
Rowid
Format is
BBBBBBB.RRRR.FFFF
Where BBBBBBB is bloack in the
database file.
RRRR is row in block
FFFF is database file
Urowid
Description
Where p is the precision and s is
the scale
e.g : decimal(4,2) o/p: 00.00
Where p is the precision and s is
the scale
e.g : decimal(4,2) o/p: 00.00
Where p is the precision and s is
the scale
e.g : decimal(4,2) o/p: 00.00
Where p is the precision and s is
the scale
e.g : decimal(4,2)
o/p: 00.00
ANSI and IBM specific type
ANSI and specific type
Floating point type
ANSI and IBM specific floating
point type
Description
Fixed-length character
length
Varible-length character
length
Variable byte string
Variable byte string
Fixed length national
character string
Variable length national
character string
Fixed length binary data
Universal row identifier.
Large Object (LOB) Data types
Data type
Range
BFILE
Upto 4 gb
BLOB
Upto 128 tb
CLOB
Upto 128 tb
NCLOB
Upto 128 tb
Date Data types
Data type
Date
Description
Used to store large binary objects in
Operating System files outside the
database
Used to store large binary objects in the
database
Used to store large binary objects in the
database
Used to store large binary objects in the
database
Range
Valid Dates range from
1st January 4712 to 31st
December 9999.
Description
Default format is ‘DD-MON-YY’.
Q-2 PL/SQL control structures
Conditional control
Iterative Control
Sequential
If..Else statement
Loop…End loop
While statement
For statement
Goto statment
Q-7 How to secure data from others users in PL/SQL.
GRANT
GRANT privileges
ON tablename
TO username
WITH Grant option
REVOKE
Revoke privileges
ON tablename
FROM username
Q-5 Advantages of PL/SQL
 SQL is the standard database language and PL/SQL is strongly integrated with SQL. PL/SQL
supports both static and dynamic SQL. Static SQL supports DML operations and
transaction control from PL/SQL block. Dynamic SQL is SQL allows embedding DDL
statements in PL/SQL blocks.
 PL/SQL allows sending an entire block of statements to the database at one time. This
reduces
network traffic and provides high performance for the applications.
 PL/SQL give high productivity to programmers as it can query, transform, and update data
in a
database.
 PL/SQL saves time on design and debugging by strong features, such as exception
handling,
encapsulation, data hiding, and object-oriented data types.
 Applications written in PL/SQL are fully portable.
 PL/SQL provides high security level.
 It offers extensive error checking.
 It offers numerous data types.
 PL/SQL provides access to predefined SQL packages.
 PL/SQL provides support for Developing Web Applications and Server Pages.
 PL/SQL provides a built-in interpreted and OS independent programming environment.
 PL/SQL can also directly be called from the command-line SQL*Plus interface.
 Direct call can also be made from external programming language calls to database.
 PL/SQL's general syntax is based on that of ADA and Pascal programming language.
 It offers a variety of programming structures.
 It supports structured programming through functions and procedures.
 It supports object oriented programming.
 It supports developing web applications and server pages.
Q-8 Data constraints
(1) Entity Data Integrity Constraints (i) Primary key (ii) Unique
(2) Domain Constraints : (i)Null and Not Null Value (iv) Check
(3) Referential Integrity Constraints
(4) User defined integrity constraints
Q-9 Aggreagate functions
Max, Min, Avg , Count, Sum
Q-8 TYPES OF CONSTRAINTS
A constraint is a property assigned to a column or the set of columns in a table which
prevent certain type of inconsistent data values. Constraints are used to enforce the data
integrity. This ensures the accuracy and reliability of data in the database.
(1)
(2)
(3)
(4)
Entity Data Integrity Constraints (i) Primary key (ii) Unique
Domain Constraints : (i)Null and Not Null Value (iv) Check
Referential Integrity Constraints
User defined integrity constraints
(1) Entity Data Integrity Constraints
(i) Primary key : It is used to identify unique values. It does not allow null and duplicate
values. A table contains only one primary key. A single column primary key is known as
simple primary key where as the multiple columns primary key is known as composite
primary key.
Primary key constraints defined at column level
Syntax: column datatype primary key
Example: create table emp (empid number primary key);
Primary key constraints defined at table level
Syntax: primary key ( column )
Example:
create table emp
(empid number, empname text(30)
primary key (empid));
(ii) Unique Value: It does not allow duplicate value but it allow multiple null values. A table
can have more than one unique key. Unique key can combine up to 16 columns in a composite
unique key.
Unique key constraints defined at column level
Syntax: column datatype unique
Example: create table emp (empid , number primary key, mobile_no text(12) unique);
Unique key constraints defined at table level
Syntax: primary key ( column )
Example:
create table emp
(empid number, mobile_no text(30)
unique (mobile_no));
(2) Domain Constraints : (i)Null and Not Null Value (ii) Check
Domain integrity enforces valid entries for a given column by restricting the type, format
or range of possible values.
(i)
Null and Not Null
Null values: By default it is null but it is different from blank and zero. It is appropriate
when actual value is not known
Not Null values: It means that column can not be left empty. If column define as not null it
means that value must be entered into the column.
Syntax: column datatype not null
Example: create table emp
(empid , number primary key,empname text(12) not null);
(ii)
Check : Business rules can be applied using check constraints. It is used to specify as
logical expression that evaluate either true or false result.
Check constrains defined at column level.
Syntax: column datatype check (logical expression)
Example: create table emp
(empid , number primary key,empname text(12) not null);
Check constrains defined at table level.
Syntax: check (logical expression)
Example: create table emp
(empid , number primary key check(<=500),
empname text(12) );
(3) Referential Integrity Constraints
Referential integrity constraints ensures that rows cannot be deleted which are used by
other records. Foreign key used to enforce referential integrity constraints. Foreign key
represent relationships between tables. A foreign key is a column whose values are derived
from the primary key of some other table.
Foreign key constrains defined at column level
Syntax: column reference tablename(column) on delete cascade
Example: create table position
(empid , number reference emp.emp_id);
Foreign key constrains defined at table level
Syntax: foreign key column references tablename(column)
Example:
(foreign empid references emp.emp_id);
(4) User defined integrity constraints:
User defined integrity constraints enforces some specific business rules that do not fall into
entity, domain or referential integrity categories.
Codd's 12 Rules
Dr Edgar F. Codd did some extensive research in Relational Model of database
systems and came up with twelve rules of his own which according to him, a
database must obey in order to be a true relational database.
These rules can be applied on a database system that is capable of managing is
stored data using only its relational capabilities. This is a foundation rule, which
provides a base to imply other rules on it.
Rule 1: Information rule
This rule states that all information (data), which is stored in the database, must be
a value of some table cell. Everything in a database must be stored in table formats.
This information can be user data or meta-data.
Rule 2: Guaranteed Access rule
This rule states that every single data element (value) is guaranteed to be accessible
logically with combination of table-name, primary-key (row value) and attributename (column value). No other means, such as pointers, can be used to access data.
Rule 3: Systematic Treatment of NULL values
This rule states the NULL values in the database must be given a systematic
treatment. As a NULL may have several meanings, i.e. NULL can be interpreted as
one the following: data is missing, data is not known, data is not applicable etc.
Rule 4: Active online catalog
This rule states that the structure description of whole database must be stored in
an online catalog, i.e. data dictionary, which can be accessed by the authorized
users. Users can use the same query language to access the catalog which they use
to access the database itself.
Rule 5: Comprehensive data sub-language rule
This rule states that a database must have a support for a language which has linear
syntax which is capable of data definition, data manipulation and transaction
management operations. Database can be accessed by means of this language only,
either directly or by means of some application. If the database can be accessed or
manipulated in some way without any help of this language, it is then a violation.
Rule 6: View updating rule
This rule states that all views of database, which can theoretically be updated, must
also be updatable by the system.
Rule 7: High-level insert, update and delete rule
This rule states the database must employ support high-level insertion, updation
and deletion. This must not be limited to a single row that is, it must also support
union, intersection and minus operations to yield sets of data records.
Rule 8: Physical data independence
This rule states that the application should not have any concern about how the
data is physically stored. Also, any change in its physical structure must not have any
impact on application.
Rule 9: Logical data independence
This rule states that the logical data must be independent of its user’s view
(application). Any change in logical data must not imply any change in the
application using it. For example, if two tables are merged or one is split into two
different tables, there should be no impact the change on user application. This is
one of the most difficult rule to apply.
Rule 10: Integrity independence
This rule states that the database must be independent of the application using it.
All its integrity constraints can be independently modified without the need of any
change in the application. This rule makes database independent of the front-end
application and its interface.
Rule 11: Distribution independence
This rule states that the end user must not be able to see that the data is distributed
over various locations. User must also see that data is located at one site only. This
rule has been proven as a foundation of distributed database systems.
Rule 12: Non-subversion rule
This rule states that if a system has an interface that provides access to low level records,
this interface then must not be able to subvert the system and bypass security and
integrity constraints.