Transcript VB Lecture 1 - American University of Beirut

CVEV 118/698
Databases
Lecture 2
Prof. Mounir Mabsout
Elsa Sulukdjian
Walid El Asmar
Introduction

All relational database development software are
similar in their way of organizing and processing
information.

MS Access is a good example of a high-level DBMS.

You can develop a full-fledged DB application using
Access alone, w/o the use of any other software
development tool.

However more powerful DB projects can be
developed by connecting to VB, VC++ etc...
Applications.
Opening a MS Access Project

This is the start-up
form.

When you create a
new project, you
will first be asked
to allocate for it a
space in the
memory.
Database Window

The database window shows all various components of a
project, of which the most important are: tables, queries, forms
and reports. From it, you can create and reach those elements.
Tables


Tables are the fundamental data containers in a database.
They are reached from the 1st tab of the database
window.
Three ways are provided to create a table:
– Design view: will require you to create and model the fields
of the table first, then work with the data.

– Wizard: will step you through the creation of a table. 
– Entering Data: will directly give you a blank datasheet, with
unlabelled columns, where to fill the data. As the table is
Saved, fields are given generic names (I.e. “Field1”, “Field2”,
etc.) that you can later edit.


Follow Smiley : work in design view! This will help you
get used to many functionalities.
Design/
datasheet Primary
view toggle key marker
Table
Design
View
Insert, Delete Field
New
rows builder
Primary key
object
Indexes Properties
Db window
Field Modeling

Upon creation of a field, you will/can model the
following main characteristics:
–
–
–
–
Field name: max of 64 characters in length (may include spaces).
Data type: Text, Number, AutoNumber, Date/Time, etc.
Description: optional description of the field for user memo.
Field Properties: set from the bottom pane of the Design View
window. See below.
Data Type

There are two main benefits in specifying data types
in a project:
– Access will prevent from putting wrong data into a field.
– Storage space will be used in a more efficient way.

Main Data Types:
– Text: Default type, allows a max of 255 characters per record.
– Number: Modeled with Field Size property (byte, integer, etc.).
– AutoNumber: Automatically assigns a unique integer to the
record upon creation; commonly used for primary keys.
– Memo: Text type that stores up to 64,000 characters.
– Date/Time: Several formats available.
– OLE Object: An ‘Object Linking and Embedding’ object is a
sound, picture, or other object such as a Word document or
Excel spreadsheet to embed or link to the database project.
Data Format

Format conforms field data to the same format when it is
entered into the datasheet.

Below, Number Format conventions:
Format
###,##0.00
Entry
Display
123456.78 123,456.78
$###,##0.00 0
$0.00
###.00%
12.3%
.123
Explanation
0 is a placeholder that displays a
digit or 0 if there is none.
# is a placeholder that displays a
digit or nothing if there is none.
% multiplies the number by 100
and added a percent sign
Data Format (Cont’d)

Below, Text and Memo Format conventions:
Format
Entry
Display
Explanation
@@@-@@@@
1234567
123-4567
@ indicates required
character or space
@@@-@@@&
123456
123-456
& indicates optional
character or space
<
HELLO
hello
< converts to lowercase
>
hello
HELLO
> converts to uppercase
@\!
Hello
Hello!
\ adds characters to the end
@;"No Data Entered" Hello
Hello
@;"No Data Entered" (blank)
No Data Entered
Controlling Data Entry


Input Masks: control value of a record and set it in a
specific format. They are similar to the Format property,
but instead display the format on the datasheet before
the data is entered.
Example:
In a telephone number field TELNUM (data type Text
or Number), the following input mask is specified:
(999) 888-7777
Thus, upon entering this attribute in a record, the blank
field would look like:
(___) ___-____
Input Mask Symbols
Symbol
0
9
#
L
?
A
a
&
C
.,:;-/
<
>
!
\
Description of Action
Digit (0-9, entry compulsory)
Digit or space (entry optional)
Digit or space (optional; blank positions appear as spaces)
Letter (A-Z compulsory)
Letter (A-Z optional)
Letter or digit (compulsory)
Letter or digit (optional)
Any character or space (compulsory)
Any character or space (optional)
Decimal point, thousands, date and time separators
All subsequent characters appear in lowercase
All subsequent characters appear in uppercase
Causes input mask to display from right to left, reversing the
default. Can be positioned anywhere in the mask.
Subsequent character is displayed literally (I.e. \& appears as &)
Controlling Data Entry (Cont’d)


Indexes: allows Access to query and sort records
faster. Set a field that is commonly searched and change
the Indexed property to Yes (Duplicates OK) if
multiple entries of the same data value are allowed or
Yes (No Duplicates) to prevent duplicates.
Field Validation Rules: specify requirements (change
word) for data entered. A customized message can be
displayed when data violating the rule setting is entered.
Examples: <> 0 to not allow zero values in the record,
and ??? to only all data strings three characters in
length.
Queries

Queries are usually developed for questions that are
regularly asked about a data.
The answer to a query is specifically displayed as an
answer table, of which the collection of records is
called a dynaset (short for Dynamic Subset).

Yet, we distinguish several types of queries:

–
–
–
–
Select: Extract data from tables based on specified values.
Parameter: user specifies criteria on which to query.
Range: Select fields/records which contain a range of values.
Group By and Crosstab: displays summarized values in a
grid form taking its rows and columns from chosen fields.
– Action: change records in a table (Delete, Update and
Append queries) or create new tables (Make-Table query).
Creating Queries in Design View


Show Table: Choose table(s) upon which the query will be built.
Query Design Window:
– Table/Query Pane: displays table(s) of concern.
– Query Design Pane: grid of definition.
Creating Queries in Design View
(cont’d)

Before developing a query, you can specify its type in design view
by clicking on the Query Type button on the toolbar.

SQL: Structured Query Language was specifically developed to
build complex queries.
It is compiled to elementary relational algebra operations (like
intersection, union, etc...), which makes it very efficient.
However it is seldom written in detail by the user, for most
manipulations can be done on the query design pane.


SQL




Generic syntax:
SELECT <field list>
FROM <table list>
[INNER JOIN ...]
[WHERE <criteria>]
[ORDER BY <field list>]
...
The WHERE clause can contain all the logical operators you
know, and more, like AND, OR, IN, LIKE, etc…
The ORDER BY clause allows sorting of the data by fields
(columns).
The INNER JOIN clause allows union of two tables with a
common column.
Forms

Access Forms are similar to VB forms, but different in
objectives: the main purpose of a form in Access is to
manipulate data in and out of the database.
Forms (Cont’d)




Most of the properties of the forms and controls are data-aware,
and are designed specifically to display fields or tabular data.
Data Binding is performed simply by setting the Record Source
property of the form to the appropriate Table or Query.
Each control can be data-bound by setting its Control Source
property to the field it corresponds to.
It is possible to include a linked sub form in a form, which is
suitable for certain cases, and simplifies the process of data entry.
What’s Next

Your new best friend 