Database
relational database
Database management system
Access
Sen Zhang
What is a databse?
• A database is a collection of information
stored on a computer in a systematic and
structured way, which should facilitate
information retrieval.
What is database management
system?
• The tool that can process database is
called database management system ( not
a hammer, an integrated software)
Relational database and relational
database management system
• Relational database is the database where
data are structured as relations (tables).
• Correspondingly, the database
management system is called RDBMS.
• Database application cares about not only
keeping track of information, but also
retrieving information.
• So, to facilitate information retrieval, a
database application has to consider how
to save data in some well defined
structures.
Why structured?
• Think about how to put your books on
shelves.
• Fast retrieval
• But slow down storing
• It is worth of the effort
• Database application is meaningful when
you need to save data and dynamically
search data as well as derive new data,
more powerful than Excel.
• It is especially useful when the application
concerns about huge amount of
information.
• One example, all transactions of Walmart.
• How does Walmart maintain all customer
transactions?
• How does walmart maintain all information about
different kinds merchandise?
• Why maintain database?
• Why you maintain your house?
• Do you need them later? If yes, then you need.
• You can find out other examples
• Excel organizes things in worksheets.
– An Excel Worksheet looks like a huge “table”.
– However, in the stricter sense, a Worksheet is
not a table. Why?
• From format point of view, it looks like a table
• From structure point of view, it is not treated like a
table.
Is Excel the right tool for database?
– To certain extend, an Excel “workbook” can be
treated as a very rudimentary “database”, but
• A workbook is
– structured at visualization level and data structure level
– but unstructured at semantic level.
» Each cell is independent from the cells in the same
column.
– Therefore is not appropriate for relational database, not the
right data.
• And Excel has not designed as a tool to process database,
– So, it is not a right tool.
Access is the right tool
– In Microsoft office suite, It is Access that is the
tool to process database stored in a kind of
specially defined data file.
– It requires data to be specially organized.
• Excel does not impose rigid structure
requirements to data in individual cells.
• Excel is not good at handling massive
amounts of data.
• Excel does not support queries from
different “tables” (actually, tables in Excel
are different from the Access’s tables!)
• It is the Access where tables are used in
the real sense (It might sound difficult to
understand at this moment, but it will be
clear at the end of the lecture) .
• We will see the differences.
Why Access is needed?
• How do you maintain information of 5000
students, 500 different classes and class
enrollment for Oneonta college?
Can you use Excel Worksheets?
• You cannot simply use Excel to accomplish the
goal for many reasons:
– different offices may keep different Excel Workbooks
for different purposes.
– redundant information will be stored, which easily
causes inconsistencies across the campus.
– the information changes all the time,
– and a large number of different reports might be
requested by different people.
– It is tedious and actually impossible to create various
excel sheets to maintain different information
separately.
– ….
Solution is to use database
• We need a better way, a centralized way
to store data, organize data, retrieve data,
and display data.
• A database is usually a collection of
centralized and organized data (or tables).
• Database is managed by database
management system.
• Microsoft Access is a powerful program to
create and manage your databases.
• Access is a database management
system, and more precisely, a relational
database management system.
• In a relational database, everything will be
organized into tables. (a table = a relation).
What is Microsoft Access?
• It has many built in features to assist you in constructing
and viewing your information.
• Access is much more involved and is a more genuine
database application than other programs such as
–
–
–
–
Microsoft Word(good at documentation),
Excel (simple spreadsheet good at small amount of data.)
PowerPoint (presentation)
FrontPage (website development).
Define some key Access
terminology
Field vs. Field value.
• Field – A single characteristic or attribute
of a person, place, object, event, or idea.
• Field value – The specific value, or
content, of a field is called the field value.
Record and table
• Record – A set of related field values.
– a Customer may have name, age, birthday,
SSN etc.
• Table – A collection of records that identify
a category of data, such as Customers,
Orders, or Inventory.
Illustration of fields, records
and a table
A Primary key
• A primary key is a field, or a collection of
fields, whose values uniquely identify each
record in a table.
– The primary key uniquely identifies a record in
the table. In other words, a primary key allows
user to distinguish one record from another in
the same table.
– In Access, a table usually has a field, or a
collection of fields to be designated as the
primary key. (Not a must, but usually we do.)
Relational database and keys
• A relational database is a collection of
tables that are related to one another
based on a common field.
• When the primary key of one table is
represented in a second table to form a
relationship, it is called a foreign key.
Relating tables using a common
field
Relational database?
• Every piece of information will be stored in relations, i.e.
tables.
• For example, student table looks like:
Student id
name
year
status
A23232
john
1988
good
A23355
john
1976
good
A34333
kathy
1979
good
Relational databse?
Course table
Course id
instructor
credit
c900
Course
name
computing
sen
3
c905
database
sen
3
Relational databse?
Enrollment table
sequence
Studentid
courseid
status
1
a23232
c900
n
2
a34333
c905
w
Relational database?
Student id
name
year
status
A23232
john
1988
good
A23355
john
1976
good
A34333
kathy
1979
good
Course id
Couse name
instructor
credit
c900
computing
sen
3
c905
database
sen
3
sequence
studentid
courseid
status
1
a23232
c900
n
2
a34333
c905
w
Several Terminologies
•
•
•
•
•
•
•
A database is a collection of related information.
An object is a member in the database such as a table, query, form, or
macro.
A table is a grouping of related data organized in fields (columns) and
records (rows) on a datasheet. By using a common field in two tables, the
data can be combined. Many tables can be stored in a single database.
A field is a column on a datasheet and defines a data type for a set of
values in a table. For a mailing list table might include fields for first name,
last name, address, city, state, zip code, and telephone number.
A record in a row on a datasheet and is a set of values defined by fields. In
a mailing list table, each record would contain the data for one person as
specified by the intersecting fields.
Design View provides the tools for creating fields in a table.
Datasheet View allows you to update, edit, and delete in formation from a
table.
More detailed Breakdown of tables
Hierarchy that Microsoft Access
uses
•
Table:A table is a collection of data about a specific topic. There
can be multiple tables in a database.
Example #1) Students
Example #2) enrollments
• Field:Fields are the different categories within a Table. Tables
usually contain multiple fields.
Example #1) Student LastName
Example #2) Student FirstName
• Datatypes:Datatypes are the properties of each field. A field only
has 1 datatype.
FieldName) Student LastName
Datatype) Text
• Values: for example a student lastname could be herbert.
Blank Access database
• Unlike Word documents, Excel worksheets,
and Power Point presentations, you must
save an Access database before you start
working on it. After selecting "Blank Access
database", you will first be prompted to
specify a location and a name for the
database.
Database Window
• The Database Window organizes all of the
objects in the database. The default tables
listing provides links for creating tables
and will list all of the tables in the database
when they have been added.
Design View
• Design View customizes the fields in the
database so that data can be entered.
Datasheet View
• The datasheet allows you to enter data
into the database
Access database wizards, pages,
and projects
• Access' wizards and layout are existing
database structures that only need data
input. Select a database type and click
OK. Name the database on the next
screen.
Forms
A form is nothing more than a graphical representation of
a table. You can add, update, delete records in your
table by using a form.
NOTE: Although a form can be named different from a
table, they both still manipulate the same information
and the same exact data. Hence, if you change a record
in a form, it will be changed in the table also.
Actually, a form and a datasheet are simply different views
of the same table.
Form view vs. Datasheet view
A form is very good to use when you have
numerous fields in a table. This way you can see
all the fields in one screen, whereas if you were
in the table view (datasheet) you would have to
keep scrolling horizontally to get the field you
desire.
A form is also very good to use when you have
numerous records in table. This way you can
concentrate on single record in one screen,
whereas if you were in the table view
(datasheet) you would have to keep scrolling
vertically to get the record you desire.
What is an Access query?
• If you want to see just a portion of the data
in a table you can create a query.
• A query is a question you ask about the
data stored in a database table.
• Access responds by displaying the data
according to your question.
– For example, if you ask to see all the
customers from New York, the response
would be to display only the records whose
state field matches with NY
Open an existing query
and create new queries
• You can open an existing query by clicking
Queries on the Objects bar and then
selecting the query you want to open.
• You can also create your own queries by
clicking New on the Database window.
• To create a new query, you can use the
Simple Query Wizard, which will bring you
through the selections you want for your
query.
Navigating a query and
sorting the results
• When you run and get the results of your
query, you can reorganize the data by
sorting the datasheet in either ascending
or descending order.
– Click the pointer anywhere in the column you
wish to sort
– Click the Sort Ascending or Sort Descending
buttons on the Query Datasheet toolbar to
sort the results in the desired sequence
• You can navigate through the records by
using the navigation buttons on the
Navigations toolbar.
Reports
• A report is an effective way to present your
data in a printed format. Because you
have control over the size and appearance
of everything on a report, you can display
the information the way you want to see it.