DB Implementation:MS Access Tables

1Database Design

RDB Implementation: Overview Tables

Translation of ER model in RDBMS constructFor data storage

• entities, attributes, relationships Forms

Data input/display user interface• e.g. data entry form, search form

For viewing, editing, entering, dynamic querying Queries

Relational algebra operations• combination of join, select, sort, filter, modify, etc.

For data retrieval & manipulation Reports

Data display output• e.g. monthly reports (set query results)

Forms can manipulate data, but reports cannot

2Database Design

RDB Implementation: Table Table is the fundamental element in a relational database.

Contains data about a particular subject• row = record = an entity (e.g., an employee, a product)

• column = field = an attribute (e.g., last name, product description)

Users seldom see tables if at all. Data entry is usually done via forms.

Main issues in table designWhat are the key attributes?

• i.e., primary & foreign keys

What is the data type for each attribute?• e.g. text, number, date, etc.

What are the properties for each attribute?• e.g. size, input/output format, range, etc.

3Database Design

MS Access Table: Data TypesText • alphanumeric data up to 255 characters.

Memo • alphanumeric data with more than 255 characters • used for notes or comments• can’t search or index on memo data type fields

Number • numeric data for fields that need to have computational operations done• Field Size = 1, 2, 4, 8, or 16 bytes

Date/Time • dates and times as 8-byte double-precision integers

Currency • monetary data as 8-byte numbers with precision to four decimal places• also used when you don't want to round values.

AutoNumber • unique values created by Access for each new record• cannot be changed once created

Yes/No • Boolean (true/false, Yes/No, On/Off)• good for checkbox type field

OLE Object • images, documents, graphs, and other objects from Office & Windows-based programs• display bitmap image of objects• less efficient & flexible than Attachment

Hyperlink • links that opens a file or a Web address (e.g. URL, email address)

Attachment • any supported files (image, spreadsheet, document, chart, etc.)• can edit as well as view files

Lookup Wizard • tool to create lookup fields in design view• lookup field = a list of values derived from existing table fields or a list (i.e. a set of values)

MS Access 2007: Data Types & Field Properties 4Database Design

MS Access Table: Field PropertiesField Size

• to set the maximum size for Text, Number, or AutoNumber data type.• affects the stored value (via rounding, truncation)

Format• to customize the display/print layout of data • does not affect the stored value (e.g. Currency $1,234.50)

Input Mask• to set the data input template to guide data entry• e.g. Short Date MM/DD/YYYY 99/99/0000;0;_

Validation Rule• to validate/restrict data entry• use with Validation Text to display message on validation failure• an expression that specify valid data values

MS Access 2007: Field Properties Quick Reference 5Database Design

Field Property: Field Size Text data type

1 to 255 Number data type

determines the precision of the number that can be stored• precision = number of significant digits

Autonumber is 4 byte

Database Design 6

Setting Storage Value (Min, Max) Significant Digits

Storage Size

Byte (0, 255) N/A 1 byte

Integer (-32,768, 32,767) N/A 2 bytes

Long Integer

(–2,147,483,648, –2,147,483,647) N/A 4 bytes

Single (–3.4*1038, +3.4*1038)  7 4 bytes

Double (–1.797*10308, 1.797*10308)  15 8 bytes

Decimal (-9.999*1027 , 9.999*1027) 28 12 bytes

Field Property: Text Format

Determines how to display the contents of data in tablesdoes not affect the stored value

For enhancing readabilitye.g., credit card/phone number@@@-@@-@@@@: 123456789 123-45-6789

Syntaxformat for non-empty text; format for empty texte.g., @;”None” display data as is, or ‘None’ when empty

Symbol Description Example

@ Required character (including space) (@@@@@): abc ( abc)

& Optional character (&&&&&): abc (abc)

< Force all characters to lowercase. <(@@@): ABC (abc)

> Force all characters to uppercase. >(@@@): abc (ABC)

[color] Display the field’s content in the named color

>(@@@)[red]: abc (ABC)

\ Display next character as entered.

&\M: abc abcM

“text” Display the text btw. quotes. &“ kg”: 16 16 kg

* Fill all blank spaces with the next character.

&*?: five five???? (display length=8)

! Fill from left instead of right. !*?: five ????five (display length=8)

MS Access 2007: Custom Format for Text & Memo data types

7Database Design

Field Property: Number Format

Pre-defined formatsCurrency e.g. displays ‘1234.567’ as ‘$1,234.56’Percent e.g. displays ‘1234.567’ as ‘123456.70%’ (requires size = “double”)Scientific e.g. displays ‘1234.567’ as ‘1.23E+3’

Examples0;(0);;”Null”

• display positive numbers normally, negative numbers in parenthesis, “Null” if the value is null

Section Description

First Format for positive numbers

Second Format for negative numbers

Third Format for zero values

Fourth Format for Null values

Symbol Description Example

0 Display a digit or 0. 00,000: 1234 01,234

# Display a digit or nothing. ##,###: 1234 1,234

% Multiply by 100 and append % sign

##.#%: 0.1234 12.3%

MS Access 2007: Custom Format for Number data types 8Database Design

Field Property: Date/Time FormatSymbol Description

d Day of the month in one or two digits (1 to 31)

dd Day of the month in two digits (01 to 31)

ddd First three letters of the weekday (Sun to Sat)

dddd Fullname of the weekday (Sunday to Saturday)

m, mm, mmm, mmmm Month equivalent to d, dd, ddd, dddd

y Number of the day in a year (1 to 366)

yy Last two digits of the year (01 to 99)

yyyy Full year (0100 to 9999)

w Day of the week (1 to 7)

h/hh, n/nn, s/ss Hours, Minutes, Seconds (1 digit/2 digit)

Pre-defined format Description

Short/Medium/Long Date

e.g. 2/28/2003, 28-Feb-03, Friday, February 28, 2003

Short/Medium/Long Time

e.g. 13:00, 1:00 PM, 1:00:00 PM

General Date Combination of Short date and Long Time as needede.g. 2/28/2003 1:00:00 PM

Example: ddd", "mmm d", "yyyy Fri, Feb 28, 2003

MS Access 2007: Custom Format for Date/Time data types

9Database Design

Field Property: Input Mask

Data input templatea set of literal and mask characters that control what can and cannot be entered in a field

• to prevent invalid data entrye.g. (999) 000-0000;;_

• data entry: (___) ___-____ (812) 855-5111• data storage: 8128551111• area code is optional

e.g. >L<??????????????• A first of last name with the first letter automatically capitalized

Section Description

First Specifies the input mask

Second Specifies whether the data is stored with the literal display characters. - 0 to include literal characters, 1 or blank to store typed characters only

Third Specifies the display character for data input positions

Symbol Description Symbol Description

0 Required digit (0 to 9) 9 Optional digit or space (0 to 9)

L Required letter ? Optional letter

A Required letter or digit a Optional letter or digit

& Required character or space C Optional character or space

# Required digit, space, or +/- Password

Display entry with *

MS Access 2007: Input Mask 10Database Design

Field Property: Format vs. Input Mask Input Mask property

to control how data is enteredaffects how data is displayed during data entrycan affect how data is stored

Format propertyto display data in a consistent formataffects how data is displayed after it is saveddoes not affect how it is stored

Decimal Places property (for Number data type)specifies the number of decimal places to displaydoes not affect how it is storedmust use Field Size property to change how a number is storedhas no effect if Format property is blank or set to “General Number”

11Database Design

Field Property: Validation Rule

Validates & Restricts data entry• Validation Text holds the error message to be displayed• use “expression” to define validation rules

– expression is a combination of operators, fields, functions, etc.– expression can be constructed using the Expression Builder

Other Data validation in MS Access• Data Type – e.g., Date/Time

• Field Size – e.g., 20 char for last name

• Required – e.g., Yes to require data entry

• Input Masks – e.g., 00000-9999 for zipcode

ExamplesValidation Rule Description

<> 0 Entry must be non-zero

>1000 Or Is Null Entry must be greater than 1000 or blank

Like “A????” Entry must be 5 characters and begin with the letter “A”

>= #1/1/96# And <#1/1/97#

Entry must be a date in 1996

MS Access 2007: Validation Rule

12Database Design

Access Table: Misc. Field PropertiesIndexed

• create internal record of the field values for searching• Access updates all of its indexes every time a table record is added or updated

– too many indexed fields can slow down data entry• Primary key field should be set to “Yes (No Duplicates)”

– exception: set composite primary key fields to “Yes (Duplicates OK)”

Required• Yes/No to indicate whether the data entry is mandatory

Allow Zero Length• Yes/No to indicate whether a zero-length string (“”) is a valid entry

Caption• label for the field (default= field name)

Default Value• value automatically entered for new records

Unicode Compression• compresses unicode character representation

– 2 bytes to 1 byte when the first byte is 0 (e.g. English)

IME Modeset Input Method Editor Mode (e.g. Hangul)

MS Access 2007: Field Properties Quick Reference 13Database Design

MS Access: Null vs. Zero-length stringNull

• A variable state indicating missing data• Information that may exist but is unknown

– i.e., “I don’t know what the value is.”– e.g., CUS_FAXNUM is set to Null initially.

• Created by pressing ENTER key in a field

Zero-length string• To handle unknown values in required fields• Information that does not exist

– i.e., “I know there is no value.”– e.g., CUS_FAXNUM is set to zero-length string after discovering that the customer has no fax.

• Created by entering two double quotes (“”) in a field

Database Design 14

MS Access: Lookup FieldLookup Field/Column

• Displays a list of choices in a combo box or list box.• The list is retrieved from another table/query or a value list.

Creating a Lookup field via Lookup Wizard

1. Select Lookup Wizard in Data Type column.– The Lookup Wizard starts

2. Select the data source in Lookup Wizard – Look up the values in a table or a query, or – Type in the values.

3. For Table/Query-based lookup field, a. Choose a table/queryb. Select fields (visible + data store)

For Value list-based lookup field,a. Enter the number of columns to include in the lookup field.b. Type the values in the grid

4. Choose the filed whose value will be used

Database Design 15 MS Access 2007: Lookup Field

MS Access: Referential Integrity Necessary Conditions

Matching field from “one” side of related tables• must be a primary key or have the Indexed property set to “Yes (No Duplicates)”.

Related fields must have the same data type.• exception: AutoNumber to Number when both have the same Field Size

EffectsCannot enter a value in the foreign key field that does not exist in the primary key of the primary tableCannot delete a record in the primary table if matching records exists in the related tableCannot change a primary key value in the primary table if that record has related records.

Cascading Updates/DeletesAllows automatic updates/deletes of all related records along with primary record

• e.g. change in primary key value in the primary table will be reflected in foreign key value of the related table

Enabled/disabled in the relationships window

16Database Design

Table How-To: Overview1. Create a table.

Table Design in Create tab

2. Add fields to the tableData TypeField Properties

3. Set the primary key

4. Save & name the table

5. Set the relationships

17Database Design

Table How-To: Creation Create a table in a new database

1. Click the Microsoft Office Button , and then click New.2. In the File Name box, type a file name for the new database. 3. To browse to a different location to save the database, click the folder icon. 4. Click Create.

• The new database opens, and a new table named Table1 is created and opens in Datasheet view.

Create a table in an existing database1. Click the Microsoft Office Button , and then click Open.2. In the Open dialog box, select the database that you want to open, and then click Open3. On the Create tab, in the Tables group, click Table Design

• A new table is inserted in the database and the table opens in Design view

18Database Design

Table How-To: Fields Add a field to an existing table

1. Open a table in Design View.

2. Type a name for the field in the Field Name column.

3. Select an appropriate data type in the adjacent Data Type column.• Text, Memo, Number, Date/Time, Yes/No, etc.

4. Set Field Properties.• Field Size, Format, Input Mask, Validation Rule, etc.• Lookup Wizard

19Database Design

Table How-To: Primary Key Set a table's primary key

1. Select the table whose primary key you want to set or change. 2. On the Home tab, in the Views group, click View, and then click Design View. 3. In the table design grid, select the field or fields that you want to use as the

primary key.• To select one field, click the row selector for the field that you want• To select more than one field, hold down CTRL, and then click the row selector for each field

4. On the Design tab, in the Tools group, click Primary Key.• A key indicator appears to the left of the field or fields that you specify as the primary key

To add an Autonumber primary key• In the Field Name column of an empty row, type a name (e.g., CustomerID)• In the Data Type column, click the drop-down arrow and click AutoNumber.

20Database Design

Table How-To: Relationships Create table relationships

1. Open a MS Access database.2. On the Database Tools tab, in the Show/Hide group, click Relationships. 3. On the Design tab, in the Relationships group, click Show Table.

• If you have not yet defined any relationships, the Show Table dialog box automatically appears.

4. Select tables and then click Add. When finished, click Close. • Click Tables in the Show Table dialog box to see only tables.

5. Drag the primary key from one table to the foreign key in the other table.• To drag multiple fields, press the CTRL key, click each field, and then drag them.

6. Verify that the field names shown in the Edit Relationships dialog box are correct. • If a field name is incorrect, click the field name and select a new field from the list.• Select the Enforce Referential Integrity check box.

7. Click Create.

21Database Design