1
Chapter 2
Reviewing Tables
and Queries
2
Chapter Objectives
• Identify the steps required to develop an
Access application
• Specify the characteristics of a welldesigned table
• Create a new Access table with its
corresponding fields, keys, indexes,
validation rules, input masks, and formats
2
Chapter Objective
• Create relationships between tables
• Create select queries, totals queries, and
action queries
• Create queries in SQL view
2
The Access Application
Development Process
• Structured systems development approach
 Includes a formal requirements specification
phase, followed by the creation of an
application blueprint, and then by programming
• Prototyping approach
 Requires the developer to build an initial
system quickly, with a shorter requirements and
design phase
2
The Access Application
Development Process
Figure 2-1
Access
application
development
process
2
Table Development
• Data constraints
 Valid values for the data
 Many can be enforced through the design of the
Access tables and relationships
2
Terminology and Rules of
Table Design
Figure 2-2
Design
view of
tblCurrentSt
udents
2
Terminology and Rules of
Table Design
• Primary key
 A field or a combination of fields that always contains a
value that uniquely identifies a row in a table
• Composite key (or multiple-field primary key)
 A primary key that consists of two or more fields
• Foreign key
 A field or a combination of fields that contains values
that are also contained by a primary key (usually, but
not always, located in another table)
 May also be null
2
Terminology and Rules of
Table Design
Figure 2-3 Query that retrieves students who need
MKTG 641 (good table design)
2
Terminology and Rules of
Table Design
Figure 2-4 Query that retrieves students who need MKTG 641 (poor
table design)
2
Terminology and Rules of
Table Design
• Points to follow when constructing tables:
 When two or more tables contain the same
fields, consider collapsing the multiple tables
into a single table
 When a table contains several similar fields,
consider creating another table that contains the
primary key of the original table plus a single
field that combines the similar fields of the
original table
2
Terminology and Rules of
Table Design
• Points to follow when constructing tables
(continued):
 If the values of two or more fields always
appear together in different rows, whether in
the same or different tables, consider creating a
new table that contains the related fields
 Creation process is called normalization
2
Normalization
• Normalization
 Process that involves splitting tables into more
than one table in an effort to control data
redundancy
• Dependency
 Exists between fields when a filed or fields
determine the value of another field
2
Normalization
Table 2-1 Normal form summary
2
Normalization
Table 2-1
Normal
form
summary
(continued)
2
Constraints in the Design
View of a Table
• Field Name column
 Contains the name of the field
• Data Type column
 Identifies the kind of data that can be stored in the field
 Enforces a constraint
• Field Size property
 Specifies how many characters or the type of number
that can be contained in the field
 Provides an additional constraint that validates the entry
of data into a field
2
Constraints in the Design
View of a Table
• Additional data types supported by Access:
 AutoNumber
 Tells Access to generate a value for the field
automatically
 ReplicationID
 Used when copies of a table are kept on more than
one computer
 Ensures that the value generated for the field is
unique across different computers
2
Constraints in the Design
View of a Table
Table 2-2
Data types
supported
by Access
2
Constraints in the Design
View of a Table
Table 2-2
Data types
supported
by Access
(continued)
2
Field Properties for Constraint
Enforcement and Formatting
• You can specify the non-null constraint for nonkey fields by choosing Yes in the Required field
property
• Non-null constraint
 Requires that all records contain a value for that field
• Zero-length string
 A valid value that is defined as “”
• Choosing No in the Allow Zero Length field
property prevents the use of zero-length strings
2
Field Properties for Constraint
Enforcement and Formatting
• Index
 Maintains a sorted list of the current values of a
field or fields
 Items in the list point to the records that have
the identified value
 Created automatically for primary keys
2
Field Properties for Constraint
Enforcement and Formatting
Figure 2-6 Indexes window of tblLevelingNeeded
2
Validation Rules and Validation
Text Field Properties
• Validation rule
 Condition that the corresponding field must satisfy
• Validation text
 Displayed if the condition of validation rule is not
satisfied
• Conditional expression
 Any statement that can be evaluated as True or False
2
Table Properties Validation
Rule
• Table Properties validation rule
 Required when a constraint requires a
comparison of the contents of two or more
fields in the same table
 Typed in the Table Properties sheet
2
Table Properties Validation
Rule
• Access allows the creation of fairly
complex validation rules
• Between, In and Like
 Operators that return True or False values
• Dlookup function
 Used in a table-level validation rule to compare
a value to values found in another table
2
Table Properties Validation
Rule
• Input mask
 Constraint mechanism
 Guides users as they type input
 Prevents users from typing incorrect values
• Input Mask Wizard
 Helps set up input masks
• Default Value field property
 Specifies the initial value of the corresponding field
2
Table Properties Validation
Rule
Table 2-4 Input Mask symbols
2
Properties Used for
Formatting
• Caption property
 Refers to the heading or prompt that will initially
appear on a form or report when the corresponding field
is included
• The default type of control that appears on a form
or report is specified through the Display
Control combo box, which is located in the
Lookup tab in the Field Properties section of the
table’s Design view
2
Properties Used for
Formatting
• Description column
 Affects a form by placing the value of the
Description column as the default status bar
text
• Format field property
 Used to indicate how stored data should be
displayed
2
Properties Used for
Formatting
Table 2-5 Symbols used in the Format property
2
Multiple Table Relationships
• Foreign keys
 Used to maintain relationships between tables
• Joining the tables
 Process of matching common attribute values
2
Multiple Table Relationships
• Referential integrity
 A constraint on data values that forces the value of a
foreign key to either:
 Match a primary key value that is contained in a row of the
related table or
 Equal null
• Explicit relationships also facilitate the use of
subdatasheets
 Allow you to display related records that are nested
within the datasheet of a table
2
Multiple Table Relationships
Figure 2-7 Some of the relationships in the Relationships
window for MU-DSci
2
Multiple Table Relationships
• Referential integrity between the primary key and
foreign key is enforced by placing a check mark in
the Enforce Referential Integrity check box
• In the Relationships dialog box, when Cascade
Update Related Fields is checked, changes in the
primary key value are automatically propagated to
the corresponding foreign key value
2
Multiple Table Relationships
Figure 2-8
Relationships
dialog box between
the
tblCurrentStudents
and
tblLevelingNeeded
2
Multiple Table Relationships
• When Cascade Delete Related Records is
checked, row deletions in the primary key table
will cause deletions of related rows in the foreign
key table
• One-to-one relationship
 Indicates that a value of the primary key can exist in
only one row as a foreign key
• One-to-many relationship
 Indicates that a value of the primary key can exist in
more than one row as a foreign key
2
Linked Tables
• To use linked tables, you must:
 Develop table definitions and table data in one
database called the source database
 Develop the queries, forms, reports, pages,
macros, and modules in a different database
called the container database
2
Query Development
• Queries
 Provide an efficient and easy method of
retrieving, manipulating, and summarizing data
 Access queries are specified in the Structured
Query Language (SQL)
• Action queries
 Make-table, update, append, and delete queries
2
Query Development
• Join lines
 Relationships predrawn between selected tables
in the query’s Design view if relationships have
been declared between tables or if Access can
guess relationships between tables
 Created by dragging a field from one table to a
field in another table
2
Query Development
Figure 2-11 Access Query menu and design grid
2
Query Development
Figure 2-12 Query showing the leveling courses needed by each
current student
2
Select and Crosstab Queries
• Select queries
 Retrieve data from other tables or queries
• Field names appear in the Field row of the grid
• Criteria row of grid
 Limits the displayed rows to those that meet a specified
condition
 Contains any statement that evaluates to True or False
2
Joins
• Inner join
 Default join type
 Includes rows only when the fields being
compared contain matching values
2
Joins
Figure 2-13 Join Properties dialog box
2
Totals Queries
• Totals queries
 Select queries that aggregate values
• The Group By item in the Total list box
 Tells Access to aggregate the other fields per
each unique value within the Group By field
2
Totals Queries
• A Where specification in the Total row
 States that the field will be tested for a criterion
before it is included in the aggregations
specified by the other columns
• Crosstab query
 Similar to a totals query, except that the former
requires at least two Group By fields
2
Action Queries
• Delete queries
 Remove rows from a table
Figure 2-16
Design view
of
qryDeleteDen
iedProspects
2
Action Queries
• Make-table queries
 Similar to select queries, except that the query results
are physically stored in a new table
• Append queries
 Similar to make-table queries, except that the results of
the select query are appended to an existing Access
table
• Update queries
 Change field values in existing rows in a table
2
Parameter Queries
• Parameter queries use parameters to substitute for
the constant values placed in the query grid
Figure
2-17
Design
view of
the
qryUpdat
ePrice
update
query
2
Chapter Summary
• Queries, forms, reports, macros, pages, and
modules display or manipulate the data contained
in the tables
• Applications should attempt to ensure data
integrity through table and relationship design
• Primary keys, input masks, validation rule, and
referential integrity can all be used to enforce data
constraints
2
Chapter Summary
• Queries are closely related to tables
• Totals and crosstab queries aggregate data
stored in the tables
• Action queries update data in the tables
• Like tables, queries are commonly used by
forms, reports, pages, macros, and modules