unit ii relational dbms + unit iv
Post on 07-Apr-2018
235 Views
Preview:
TRANSCRIPT
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 1/16
Relational model was first introduced by Ted Codd of IBM Research in 1970. The model uses the concept
of a mathematical relation as its basic building block and has its theoretical basis in set theory and first
order predicate logic. Examples of relational model includes: Oracle( from Oracle), SQL Server, Ms
Access( from Microsoft)
Data models that preceded the relational model include hierarchical and network models.
Relational Model Concepts: The relational model represents the database as a collection of relations. A
relation is a named, two-dimensional table of data. Each row in the table represents a collection of
related data values.
Terminology
Domain: a domain D is a set of atomic values. Atomic means that each value in the domain is indivisible
. In other words domain refers to the description of an attribute's allowed values. A common method of
specifying a domain is to specify a data type from which the data values forming the domain are drawn.
E.g. the data type for the domain Phone Numbers can be declared as of character strings, Data type for
employee age is an integer number between 15 and 80.
Relation Schema: A relation schema R denoted by R(A1,A2,A3,..,AN) is made up of a relation name R
and a list of attributes A1, A2,,AN. Each attribute Ai is the name of a role played by some domain D in
the relation schema R. D is called the domain of Ai and is denoted by dom(Ai). A relation schema is used
to describe a relation, R is called the name of the relation.
Meta Data: A metadata / data dictionary is defined as the data about the data. It is also known as
system catalog. The system catalog integrates the metadata.
Metadata is the data that describes the objects in the database. So it is easier to access those objects. It
describes the database structure, constraints, applications and size of data types etc.
Degree ( Arity) of a relation: Degree of a relation is the number of attributes n of its relation schema.
E.g. Student ( RollNo, Name, HomePhone. Address, Age, Percentage)
Relation Name: Student
Attributes: RollNo,Name,Homephone,Address,Age,percentage
Degree of the relation: 6
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 2/16
Relation : A relation r of the relation schema R(A1,A2,A3,..,AN) also denoted by r( R) , is a set of n-tuples
r={t1, t2, t3,tm}. Each n-tuple is an ordered list of n values t=<v1,v2,v3,vn>, where each value vi,
1<=i<=n, is an element of dom(Ai)or is a special null value. The ith
value in tuple t, which corresponds to
the attribute Ai , is referred to as t[Ai].
In other words ,a relation r(R) is a ,mathematical relation of degree n on the domain dom(A1),dom(A2),,dom(An) which is a subset of the Cartesian product of the domains that define R:
r (R) (dom(A1) X dom (A2) XXdom(An))
Characteristics of Relations
1) Ordering of tuples in a Relation: Tuples in a relation do not have any particular order.
2) Ordering of values within a tuple: Since a tuple is an ordered list of n values, so the ordering of
values in the tuple and hence the attributes in a relation schema is important.
3) Values and Nulls in the tuple: Each value in a tuple is an atomic value that is not divisible into
components within the framework of the basic relational model. A special value , called Null
value is used to represent values of attributes that may be unknown or may not apply to the
tuples.
4) Cardinality of a Relation: No: of tuples in the relation.
Types of keys
A key is an attribute (also known as column or field) or a combination of attribute that is used to identify
records.
The various types of keys are mentioned below, (For examples let suppose we have an Employee Table
with attributes ID , Name ,Address , Department_ID ,Salary)
Super Key: An attribute or a combination of attribute that is used to identify the records uniquely is
known as Super Key. A table can have many Super Keys.
E.g. of Super Key
1 ID
2 ID, Name
3 ID, Address
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 3/16
4 ID, Department_ID
5 ID, Salary
6 Name, Address
7 Name, Address, Department_ID So on as any combination which can identify the records
uniquely will be a Super Key.
Candidate key: It can be defined as minimal Super Key or irreducible Super Key. In other words an
attribute or a combination of attribute that identifies the record uniquely but none of its proper
subsets can identify the records uniquely.
E.g. of Candidate Key
1 ID
2 Name, Address
For above table we have only two Candidate Keys (i.e. Irreducible Super Key) used to identify the
records from the table uniquely. ID Key can identify the record uniquely and similarly combination of
Name and Address can identify the record uniquely, but neither Name nor Address can be used to
identify the records uniquely as it might be possible that we have two employees with similar name
or two employees from the same house.
Thus the Key constraints are:
Two distinct tuples in any state of the relation cannot have identical values for all the
attributes in the key.
It is a minimal superkey- that is, a superkey from which we cannot remove any
attributes and still have the uniqueness constraint in condition 1.
Primary Key: A Candidate Key that is used by the database designer for unique identification of each
row in a table is known as Primary Key. A Primary Key can consist of one or more attributes of a
table.
E.g. of Primary Key - Database designer can use one of the Candidate Key as a Primary Key. In this
case we have ID and Name, Address as Candidate Key, we can consider ID Key as a Primary
Key.
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 4/16
Alternate Key: Alternate Key can be any of the Candidate Keys except for the Primary Key.
E.g. of Alternate Key is Name, Address as it is the only other Candidate Key which is not a Primary
Key.
Secondary Key : The attributes that are not the Super Key but can be still used for identification of
records (not unique) are known as Secondary Key.
E.g. of Secondary Key can be Name, Address, Salary, Department_ID etc. as they can identify the
records on the basis of Name, address, Salary and Department.
Composite Key : If we use multiple attributes to create a Primary Key then that Primary Key is called
Composite Key (also called a Compound Key or Concatenated Key).
E.g. of Composite Key, if we have used Name, Address as a Primary Key then it will be our
Composite Key.
Foreign Key A foreign key is an attribute or combination of attribute in one base table that points
to the candidate key (generally it is the primary key) of another table. Foreign key can be used to
cross-reference tables.
The purpose of the foreign key is to ensure referential integrity of the data i.e. only values that are
supposed to appear in the database are permitted.
A set of attributes FK in a relation schema R1 is a foreign key of R1 that references relationR2 if it
satisfies the following two rules:
1) The attributes in FK have the same domain as the primary key attributes PK of R2 ; the
attributes FK are said to reference or refer to the relation R2.
2) A value of FK in a tuple t1 of the current state r1(R1) either occurs as a value of PK for some
tuple t2 in the current state r2(R2) or is null.
E.g. of Foreign Key Let consider we have another table i.e. Department Table with Attributes
Department_ID, Department_Name, Manager_ID, Location_ID with Department_ID as an
Primary Key. Now the Department_ID attribute of Employee Table can be defined as the Foreign Key
as it can reference to the Department_ID attribute of the Departments table (the referenced orparent table), a Foreign Key value must match an existing value in the parent table or be NULL.
Relational Database Schema: A relational database schema S is a set of relation schemas S= {R1, R2,
Rm} and a set of integrity constraints IC. A database state that does not obey all the integrity constraints
is called an invalid state, and the state that satisfies all the constraints in IC is called a valid state.
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 5/16
Creating relations using SQL
The CREATE TABLE statement is used to specify a new base relation by giving it a name and specifying its
attributes and initial constraints. The attributes are specified first, and each attribute is given a name, a
data type to specify its domain of values, and any attribute constraints such as NOT NULL. The key,
entity integrity and referential integrity constraints can be specified within the CREATE TABLE statementafter the attributes are declared.
Because SQL permits NULL as attribute values, a constraint NOT NULL may be specified if NULL is not
permitted for a particular attribute. It is also possible to define a default value for an attribute by
appending the clause DEFAULT <value> to an attribute definition. The default value is included in any
new tuple if an explicit value is not provided for that attribute.
Syntax :create table table name ( attr name type, attr name type)
E.g.
Create table Students( Roll No Char(20) DEFAULT 1, name char(30) NOT NULL, percentage Real)
Integrity Constraints: An integrity constraint (IC) is a condition specified on a database schema and
restricts the data that can be stored in an instance of the database. A database state that does not obey
all the integrity constraints is called an invalid state, and the state that satisfies all the constraints in IC is
called a valid state. All integrity constraints should be specified on the relational database schema,
hence DDL includes provisions for specifying the various types of constraints so that the DBMS can
automatically enforce them.
Many kinds of integrity constraints can be specified in the Relational model:
y Domain Constraints
y Key Constraints
y Entity Integrity constraint
y Referential Integrity constraint ( specified between 2 attributes) Foreifn key
Domain Constraint: specify that within each tuple, the value of each attribute A must be atomic value
from the domain(A).
A domain constraint specified by the data type of each attribute in the Create table command.
E.g.
Create table Students( Roll No Char(20), name char(30), percentage Real)
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 6/16
Alternatively a domain can be declared, and the domain name can be used with the attribute
specifications.
E.g.
Create Domain ageval as Integer Default 18 Check (ageval>=18 and ageval <=21)
After defining a domain ageval we can use it as a data type as shown below.
Create table Student ( Roll NO Char(10), Name Char(20), Age ageval)
Key Constraint: A key of a database must satisfy the following two conditions:
Two distinct tuples in any state of the relation cannot have identical values for all the
attributes in the key.
It is a minimal superkey- that is, a superkey from which we cannot remove any
attributes and still have the uniqueness constraint in condition 1.
Primary key clause is used to specify one or more attributes that make the primary key of the relation. If
the primary key has a single attribute, the clause can follow the attribute directly.
E.g.
Create table Students( Roll No Char(20),
name char(30),
percentage Real)
CONSTRAINT STUKEY PRIMARY KEY (Roll No))
OR
Create table Students( Roll No Char(20) PRIMARY KEY,
name char(30),
percentage Real))
Domain
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 7/16
Entity Integrity constraint: The Integrity constraint states that no primary key value can be null. This is
because the primary key value is used to identify individual tuples in a relation. Having Null values for
the primary key implies that we cannot identify some tuples.
Referential Integrity Constraint ( Foreign Key Constarint): The referential integrity constraint is
specified between two relations and is used to maintain the consistency among tuples in the two
relations. Referential integrity involves the concept of Foreign key. The FOREIGN KEY constraint is used
to prevent actions that would destroy links between tables.
The FOREIGN KEY constraint also prevents that invalid data from being inserted into the foreign key
column, because it has to be one of the values contained in the table it points to.
Referential integrity constraint is specified via the Foreign Key clause.
Create table Enrolled( Roll No Char(20),
CourseID char(30),
Grade Char(10),
PRIMARY KEY (Roll No), CourseID)
FOREIGN KEY (Roll No) REFERENCES Students)
Enforcing Integrity Constraints:
ICs are specified when a relation is created and enforced when a relation is modified. If an insert,
update and delete command causes a violation, it is rejected.
For example consider the following two relations :
Create table Students( Roll No Char(20),
name char(30),
percentage Real)
UNIQUE ( name);
CONSTRAINT STUKEY PRIMARY KEY (Roll No))
Create table Enrolled( Roll No Char(20),
CourseID char(30),
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 8/16
Grade Char(10),
CONSTRAINT STUKEY PRIMARY KEY (Roll No), CourseID)
FOREIGN KEY (Roll No) REFERENCES Students(Roll No))
Some examples of Violations of ICs
Insertions:
into student two rows with same Roll no / a row with null value for Roll no ( Violation of Primary key
constraint)
into enrolled a row with Roll no not in student (Violation of foreign key constraint)
Deletions : a row from student which is referred to in Enrolled relation. (Referential Integrity violation)
Update: Roll No of a student , referred to in the Enrolled relation (Referential Integrity violation)
In case of integrity violation, several actions can be taken:
y Cancel the operation that causes the violation (REJECT option)
y Perform the operation but inform the user of the violation
y Trigger additional updates so the violation is corrected (CASCADE option, SET NULL option)
These actions are specified as a part of Foreign key declaration:
1) Restrict : means that the action( DELETE or UPDATE) is to be rejected.
2) Cascade : cascade the deletion by deleting tuples that reference the tuple that is being deleted
3) Set Default: modify the referencing attribute values that cause the violation; each such value is
either set to Null or changed to reference another valid tuple.
SQL
The name SQL is derived from Structured Query language and was designed and implemented at IBM
research. SQL is the standard language for commercial relational DBMS. SQL is a comprehensive
database language. It has statements for data definition, query and update. Hence it is both a DDL and a
DML.
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 9/16
SQL DDL
DDL
1) Create table
2) Drop table
3) Alter table
Create Table: The CREATE TABLE statement is used to specify a new base relation by giving it a name
and specifying its attributes and initial constraints. The attributes are specified first, and each attribute is
given a name, a data type to specify its domain of values, and any attribute constraints such as NOT
NULL. The key, entity integrity and referential integrity constraints can be specified within the CREATETABLE statement after the attributes are declared.
Because SQL permits NULL as attribute values, a constraint NOT NULL may be specified if NULL is not
permitted for a particular attribute. It is also possible to define a default value for an attribute by
appending the clause DEFAULT <value> to an attribute definition. The default value is included in any
new tuple if an explicit value is not provided for that attribute.
Syntax :create table table name ( attr name type, attr name type)
E.g.
Create table Students( Roll No Char(20) DEFAULT 1, name char(30) NOT NULL, percentage Real)
DROP TABLE: If a base table within a schema is not needed any longer, the relation and its definition can
be deleted by using DROP TABLE command. The relation can no longer be used in queries, updates, or
any other commands since its description no longer exists
Syntax: DROP TABLE TABLE NAME
There are two drop behavior option:
y Cascade : all foreign key constraints and views that reference the table are dropped
automatically from the schema along with the table itself
E.g. DROP TABLE EMP CASCADE
y Restrict: a table is dropped only if it is not referenced in any constraints.
E.g. DROP TABLE EMP RESTRICT
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 10/16
Alter table: Alter table modifies the structure of an existing table. It is used to:
a) Add new columns
b) Drop existing columns
c) Modify existing column
d) Add integrity constraints
e) Drop existing constraints
E.g.
Alter table Students Add Address(30)
Alter table Students Modify Roll No Char(15)
Alter table Students Modify Roll No Set Default 1001
Alter table Students Add Constraint chkage check (Age>=18 and Age<=21)
Alter table Drop Percentage
To drop a column we must use either CASCADE or RESTRICT for drop behavior.
If Cascade is used all constraints and views that reference the column are dropped automatically from
the schema.
If Restrict is used the column is dropped only if it is not referenced in any constraints or views.
DML: There are three SQL commands to modify the database:
1) Insert
2) Delete
3) Update
Insert : In its simplest form, it is used to add one or more tuples to a relation. Attribute values should be
listed in the same order as the attributes were specified in the CREATE TABLE command.
Example:
Suppose a table Student is created using the Create table command as follows:
Create table Students( Roll No Char(20),
name char(30),
percentage Real)
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 11/16
UNIQUE ( name);
CONSTRAINT STUKEY PRIMARY KEY (Roll No))
Tuples can be inserted into Student table using the following Insert statements:
Insert into Student Values ( 11,Rita,83)
An alternate form of INSERT specifies explicitly the attribute names that correspond to the values in the
new tuple
Attributes with NULL values can be left out
Example: Insert a tuple for a new Student for whom we only know the Roll No and Name attributes.
Insert into Student( Roll No, Name) Values (23, Sita)
Delete: Removes tuples from a relation. It includes a WHERE-clause to select the tuples to be deleted.
Tuples are deleted from only one table at a time (unless CASCADE is specified on a referential integrity
constraint)
A missing WHERE-clause specifies that all tuples in the relation are to be deleted; the table then
becomes an empty table. The number of tuples deleted depends on the number of tuples in the relation
that satisfy the WHERE-clause.
Examples:
Delete From Student where Roll No=11
Delete from student where Name=Sita
Delete from student
Update: Used to modify attribute values of one or more selected tuples. A WHERE-clause selects the
tuples to be modified. An additional SET-clause specifies the attributes to be modified and their new
values. Each command modifies tuples in the same relation
Update Student Set Name=Riya Where Roll No=11
SQL queries from book which will include:
1) Syntax
2) To learn how to write SQL queries (practice as many questions as possible, including previous
years)
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 12/16
3) Aggregate functions //IMPORTANT
4) String comparision //IMPORTANT
5) Order By clause //IMPROTANT
6) Group by clause (including having) //IMPORTANT
7) Use of *, Distinct,Exists, Not exists, //IMPORTANT
8) Set operations ( UNION , INTERSECT, MINUS) //IMPORTANT
9) What is meant by union compatibility between relations. //IMPORTANT
Views: A view in SQL is a single table that is derived from other tables. These other tables could be base
tables or previously defined views. A view is considered as a virtual table, in contrast to base table
whose tuples are actually stored in the database. This limits the possible update operations that can be
applied to views., but allows full query operations.
Uses of Views:
1. It can be used to hide sensitive columns.
2. It can be used to hide complex queries involving multiple tables.
3. Views that are created with a check option, prevents updating of other rows and columns.
4. It can simplify complex operations on the base relations.
The command to specify a view is CREATE VIEW. The view is given a view name, a list of attribute names
and a query to specify the contents of the view.
E.g.
CREATE VIEW WORKS_ON_NEW
AS SELECT FNAME,LNAME, PNAME, HOURS
FROM EMPLOYEE, PROJECT, WORKS_ON
WHERE ENO=EENO AND PNO=PNUMBER
We can specify SQL queries on a newly create view
SELECT FNAME, LNAME FROM WORKS_ON_NEW
WHERE PNAME=Seena
When no longer needed, a view can be dropped:
DROP WORKS_ON_NEW
Update of views is complicated and can be ambiguous. In general,
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 13/16
i) A view with a single table is updatable if the view attributes contain the primary key of the
base table, as well as all the attributes with the NOT NULL constraint that do not have
default values specified.
ii) Views defined on multiple tables using joins are generally not updateable.
iii) Views defined using grouping and aggregate functions are not updatable.
Microsoft Access Data Types
Data type Description Storage
Text Use for text or combinations of text and numbers. 255 characters maximum Upto 255characters
Memo Memo is used for larger amounts of text. Stores up to 65,536 characters. Upto 63999
characters
Byte Allows whole numbers from 0 to 255 1 byte
Integer Allows whole numbers between -32,768 and 32,767 2 bytes
Long Allows whole numbers between -2,147,483,648 and 2,147,483,647 4 bytes
Single Single precision floating-point. Will handle most decimals 4 bytes
Double Double precision floating-point. Will handle most decimals 8 bytes
Currency Use for currency. Holds up to 15 digits of whole dollars, plus 4 decimal places. 8 bytes
AutoNumber AutoNumber fields automatically give each record its own number, usuallystarting at 1
4 bytes
Date/Time Use for dates and times 8 bytes
Yes/No A logical field can be displayed as Yes/No, True/False, or On/Off. 1 bit
Ole Object Can store pictures, audio, video up to 1GB
Hyperlink Contain links to other files, including web pages
Lookup Wizard Let you type a list of options, which can then be chosen from a drop-down list 4 bytes
Codds Rules: Codd's twelve rules are a set of thirteen rules (numbered zero to twelve) proposed by
Edgar F. Codd, designed to define what is required from a database management system in order for it
to be considered relational, i.e., a relational database management system (RDBMS).
The rules
Rule 0: The system must qualify as rel ational , as a database, and as a management syst em.
For a system to qualify as a relational database management system (RDBMS), it system must use its
rel ational facilities (exclusively) to manage the database.
Rule 1: The infor mation rule:
All information in the database is to be represented in one and only one way, namely by values in
column positions within rows of tables.
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 14/16
Rule 2: The guar ant eed access rule:
All data must be accessible. This rule is essentially a restatement of the fundamental requirement for
primary keys. It says that every individual scalar value in the database must be logically addressable by
specifying the name of the containing table, the name of the containing column and the primary key
value of the containing row.
Rule 3: Syst ematic t reatment of null values:
The DBMS must allow each field to remain null (or empty). Specifically, it must support a representation
of "missing information and inapplicable information" that is systematic, distinct from all regular values
and independent of data type. It is also implied that such representations must be manipulated by the
DBMS in a systematic way.
Rule 4: Activ e onl ine catal og based on the rel ational mod el :
The system must support an online, inline, relational catalog that is accessible to authorized users by
means of their regular query language. That is, users must be able to access the database's structure
(catalog) using the same query language that they use to access the database's data.
Rule 5: The comprehensiv e data subl anguage rule:
The system must support at least one relational language that
1. Has a linear syntax
2. Can be used both interactively and within application programs,
3. Supports data definition operations (including view definitions), data manipulation operations(update as well as retrieval), security and integrity constraints, and transaction management
operations (begin, commit, and rollback).
Rule 6: The vi ew u pdating rule:
All views that are theoretically updatable must be updatable by the system.
Rule 7: High-lev el inser t, u pdat e , and d elet e:
The system must support set-at-a-time inser t , u pdat e, and d elet e operators. This means that data can be
retrieved from a relational database in sets constructed of data from multiple rows and/or multiple
tables. This rule states that insert, update, and delete operations should be supported for any
retrievable set rather than just for a single row in a single table.
Rule 8: Physical data ind e pend ence:
Changes to the physical level must not require a change to an application based on the structure.
Rule 9: Logical data ind e pend ence:
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 15/16
Changes to the logical level (tables, columns, rows, and so on) must not require a change to an
application based on the structure. Logical data independence is more difficult to achieve than physical
data independence.
Rule 10: Int egr ity ind e pend ence:
Integrity constraints must be specified separately from application programs and stored in the catalog. It
must be possible to change such constraints as and when appropriate without unnecessarily affecting
existing applications.
Rule 11: Dist r ibution ind e pend ence:
The distribution of portions of the database to various locations should be invisible to users of the
database. Existing applications should continue to operate successfully:
1. when a distributed version of the DBMS is first introduced; and
2. when existing distributed data are redistributed around the system.
Rule 12: The nonsubv er sion rule:
If the system provides a low-level (record-at-a-time) interface, then that interface cannot be used to
subvert the system, for example, bypassing a relational security or integrity constraint.
Database Objects: Database objects are the components that save and query information. A database
contains several objects that are used to provide storage and display large, relational data. The main
objects of a database are tables, stored procedures, views, users and functions.
Tables: All data is stored in tables. When we create a new table, MS Access asks us to define fields
(column headings), giving each a unique name, and telling Access the data type. Once we have defined a
table's structure, we can enter data. Each new row that we add to the table is called a record. To define
relationships between tables:
in Access 2007 or later: Database Tools | Relationships,
in Access 95 2003: Tools | Relationships,
Queries: Queries retrieve the data based on specific criteria. This is the most important element of SQL,which is performed with the declarative SELECT statement. SELECT retrieves data from one or more
tables, or expressions. With a query, we can display the records that match certain criteria (e.g. all the
members called "Barry"), sort the data (e.g. by Surname), and even combine data from different tables.
Queries allow the user to describe desired data, leaving the database management system (DBMS)
responsible for planning, optimizing, and performing the physical operations necessary to produce that
result as it chooses.
8/6/2019 Unit II Relational DBMS + Unit IV
http://slidepdf.com/reader/full/unit-ii-relational-dbms-unit-iv 16/16
Forms: A form is a database object that us can use to enter, edit, or display data from a table or a query.
We can use forms to control access to data, such as which fields or rows of data are displayed. An
effective form speeds the use of the database, because people don't have to search for what they need.
A visually attractive form makes working with the database more pleasant and more efficient, and it canalso help prevent incorrect data from being entered.
Create a form by using the Form tool: ( Ms Access 2007)
We can use the Form tool to quickly create a single item form. This type of form displays information
about one record at a time.
1. In the Navigation Pane, click the table or query that contains the data that you want to see on the
form.
2.
On the Create tab, in the Forms group, click Form.
Access creates the form and displays it in Layout view. In Layout view, you can make design
changes to the form while it is displaying data. For example, you can adjust the size of the text
boxes to fit the data.
3. To begin working with the form, switch to Form view:
On the Home tab, in the Views group, click View, and then click Form View
Reports: A database report presents information retrieved from a table or query in a preformatted, attractive
manner.
Create a report by using the Report tool
The Report tool provides the fastest way to create a report, because it generates a report immediately
without prompting us for information. The report displays all the fields from the underlying table or
query. The Report tool may not create the final, polished product that we ultimately want, but it is quite
useful as a means to quickly look at the underlying data. We can then save the report and modify it in
Layout view or Design view so that it better serves your purposes.
1. In the Navigation Pane, click the table or query on which you want to base the report.
2. On the Create tab, in the Reports group, click Report.
Access builds the report and displays it in Layout view.
After viewing the report, we can save it and then close both the report and the underlying table or query
that we used as a record source. The next time that we open the report, Access will display the most
recent data from your record source
top related