1Chapter 2Chapter 2

Reviewing Tables and Queries

Reviewing Tables and Queries

2Chapter ObjectivesChapter Objectives

• Identify the steps required to develop an Access application

• Specify the characteristics of a well-designed table

• Create a new Access table with its corresponding fields, keys, indexes, validation rules, input masks, and formats

2Chapter ObjectiveChapter Objective

• Create relationships between tables

• Create select queries, totals queries, and action queries

• Create queries in SQL view

2 The Access Application Development Process

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

The Access Application Development Process

Figure 2-1 Access application development process

2Table DevelopmentTable 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

Terminology and Rules of Table Design

Figure 2-2 Design view of tblCurrentStudents

2 Terminology and Rules of Table Design

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

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

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

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

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 fieldsCreation process is called normalization

2NormalizationNormalization

• 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

2NormalizationNormalization

Table 2-1 Normal form summary

2NormalizationNormalization

Table 2-1 Normal form summary (continued)

2 Constraints in the Design View of a Table

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

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

ReplicationIDUsed when copies of a table are kept on more than

one computerEnsures that the value generated for the field is

unique across different computers

2 Constraints in the Design View of a Table

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

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

Field Properties for Constraint Enforcement and Formatting

• You can specify the non-null constraint for non-key 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

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

Field Properties for Constraint Enforcement and Formatting

Figure 2-6 Indexes window of tblLevelingNeeded

2 Validation Rules and Validation Text Field Properties

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

• 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

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

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 Properties Validation Rule

Table 2-4 Input Mask symbols

2 Properties Used for Formatting

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

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

Properties Used for Formatting

Table 2-5 Symbols used in the Format property

2Multiple Table RelationshipsMultiple Table Relationships

• Foreign keys Used to maintain relationships between tables

• Joining the tables Process of matching common attribute values

2Multiple Table RelationshipsMultiple 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

2Multiple Table RelationshipsMultiple Table Relationships

Figure 2-7 Some of the relationships in the Relationships window for MU-DSci

2Multiple Table RelationshipsMultiple 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

2Multiple Table RelationshipsMultiple Table Relationships

Figure 2-8 Relationships dialog box between the tblCurrentStudents and tblLevelingNeeded

2Multiple Table RelationshipsMultiple 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

2Linked TablesLinked 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

2Query DevelopmentQuery 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

2Query DevelopmentQuery 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

2Query DevelopmentQuery Development

Figure 2-11 Access Query menu and design grid

2Query DevelopmentQuery Development

Figure 2-12 Query showing the leveling courses needed by each current student

2Select and Crosstab QueriesSelect 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

2JoinsJoins

• Inner join Default join type Includes rows only when the fields being

compared contain matching values

2JoinsJoins

Figure 2-13 Join Properties dialog box

2Totals QueriesTotals 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

2Totals QueriesTotals 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

2Action QueriesAction Queries

• Delete queries Remove rows from a table

Figure 2-16 Design view of qryDeleteDeniedProspects

2Action QueriesAction 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

2Parameter QueriesParameter Queries

• Parameter queries use parameters to substitute for the constant values placed in the query grid

Figure 2-17 Design view of the qryUpdatePrice update query

2Chapter SummaryChapter 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

2Chapter SummaryChapter 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