Access-6.ppt 558KB Mar 29 2010 04:55:15 AM
Exploring Microsoft Access
Chapter 6
Many-to-Many Relationships: A
More Complex System
Objectives (1 of 2)
• Define and explain a many-to-many
relationship
• Use Cascade Update and Cascade Delete
• Explain how the AutoNumber field
simplifies entering new records
Objectives (2 of 2)
• Create a main farm and subform based on a
query
• Create a parameter query
• Use aggregate functions
• Use Get External Data command
Overview (1 of 2)
• More database design practice
• Extends relational database concepts
including one-to-many and many-to-many
relationships
• Use AutoNumber to simplify record
creation
Overview (2 of 2)
• Extends subform and query information
from related tables
• Create forms based on multiple-table
queries
• Create a parameter query
• Create queries with built-in aggregate
functions
Many-to-Many Relationships
• A many-to-many relationship requires an
additional table that has a one-to-many
relationship to each of the related tables
• The primary key of the additional table is
the combination of the primary keys of the
related tables
Implementing Many-To-Many
Relationships
Many-to-many
relationship is
implemented by a
pair of one-tomany
relationships
Enforce Referential
Integrity is selected
Cascade Delete Related
Records is selected
Referential Integrity
• Ensures records in related tables are consistent with
one another
• Prevents adding a record to a related table with an
invalid foreign key
• Prevents deleting a record in the primary table when
there are corresponding records in the related table
Cascaded Deletion
• When a record in the primary table is
deleted, Access simultaneously deletes the
corresponding records in the related table
Cascaded Updating
• When the primary key in the primary table
is updated, Access automatically updates
the value in the corresponding records in
the related table
Subforms, Queries, and
AutoLookup
• Main and subforms based on queries:
- display of information from multiple
tables
- display records other than by primary key
• AutoLookup will find corresponding data
after unique ID is entered
Main Form and Subform
Main form has
fields
from Orders and
Customers
tables
Subform has fields from Order Details and Products tables
Designing a main and subform
Main form Detail
Subform
Detail
Parameter Queries
• Prompts the user for criteria when executed
• The prompt is enclosed in square brackets in
the query design grid
• A parameter query may prompt for any
number of variables
Parameter Query
Users are prompted
with a dialog box when the
query is executed
Enter the prompt in square brackets in the Criteria field
Total Queries
• Total Queries perform calculations on a group of
records
• Total row – Contains either Group by or aggregate
entry
• Group By – Records in the dynaset are to be
grouped according to the like values
• Sum Function – Specifies math to be performed on
that field for each group of records
Adding Tables
Existing tables and
relationships are unaffected
by addition of new table
Chapter 6 Summary (1 of 2)
• A many-to-many relationship requires an
additional table
• Many-to-many is implemented with a pair
of one-to-many relationships
• Enforce referential integrity to prevent
errors
• Base forms and subforms on queries
Chapter 6 Summary (2 of 2)
• Parameter query uses prompts
• Aggregate functions perform calculations
on groups of records
• New tables may be added at any time
without affecting data in the existing tables
Chapter 6
Many-to-Many Relationships: A
More Complex System
Objectives (1 of 2)
• Define and explain a many-to-many
relationship
• Use Cascade Update and Cascade Delete
• Explain how the AutoNumber field
simplifies entering new records
Objectives (2 of 2)
• Create a main farm and subform based on a
query
• Create a parameter query
• Use aggregate functions
• Use Get External Data command
Overview (1 of 2)
• More database design practice
• Extends relational database concepts
including one-to-many and many-to-many
relationships
• Use AutoNumber to simplify record
creation
Overview (2 of 2)
• Extends subform and query information
from related tables
• Create forms based on multiple-table
queries
• Create a parameter query
• Create queries with built-in aggregate
functions
Many-to-Many Relationships
• A many-to-many relationship requires an
additional table that has a one-to-many
relationship to each of the related tables
• The primary key of the additional table is
the combination of the primary keys of the
related tables
Implementing Many-To-Many
Relationships
Many-to-many
relationship is
implemented by a
pair of one-tomany
relationships
Enforce Referential
Integrity is selected
Cascade Delete Related
Records is selected
Referential Integrity
• Ensures records in related tables are consistent with
one another
• Prevents adding a record to a related table with an
invalid foreign key
• Prevents deleting a record in the primary table when
there are corresponding records in the related table
Cascaded Deletion
• When a record in the primary table is
deleted, Access simultaneously deletes the
corresponding records in the related table
Cascaded Updating
• When the primary key in the primary table
is updated, Access automatically updates
the value in the corresponding records in
the related table
Subforms, Queries, and
AutoLookup
• Main and subforms based on queries:
- display of information from multiple
tables
- display records other than by primary key
• AutoLookup will find corresponding data
after unique ID is entered
Main Form and Subform
Main form has
fields
from Orders and
Customers
tables
Subform has fields from Order Details and Products tables
Designing a main and subform
Main form Detail
Subform
Detail
Parameter Queries
• Prompts the user for criteria when executed
• The prompt is enclosed in square brackets in
the query design grid
• A parameter query may prompt for any
number of variables
Parameter Query
Users are prompted
with a dialog box when the
query is executed
Enter the prompt in square brackets in the Criteria field
Total Queries
• Total Queries perform calculations on a group of
records
• Total row – Contains either Group by or aggregate
entry
• Group By – Records in the dynaset are to be
grouped according to the like values
• Sum Function – Specifies math to be performed on
that field for each group of records
Adding Tables
Existing tables and
relationships are unaffected
by addition of new table
Chapter 6 Summary (1 of 2)
• A many-to-many relationship requires an
additional table
• Many-to-many is implemented with a pair
of one-to-many relationships
• Enforce referential integrity to prevent
errors
• Base forms and subforms on queries
Chapter 6 Summary (2 of 2)
• Parameter query uses prompts
• Aggregate functions perform calculations
on groups of records
• New tables may be added at any time
without affecting data in the existing tables