Download Access Tutorial 3

Microsoft Access 2002
Tutorial 3 – Querying a Database
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The Query Window in Design View
 The Query window in Design view allows you
to …
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can specify which fields you want to be
included in your query results.
control what records are displayed in the
query by specifying select query criteria.
 Each column in the design grid represents a
field that will be used in the query.
 You can run the query at anytime to view the
results according to the current specifications.
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Add Fields To a Query in Design View
 The design grid is used to specify the fields and
records you want to see.
 Add fields to the design grid by double-clicking the
field in the field list or by dragging the field to the
design grid.
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Remember that the results of a query provide a
temporary view of the data
The contents displayed in a query are a result of the
fields you select and the criteria you specify in the
query design grid
 When you use the query design window, you use
Query By Example (QBE). When you use QBE, you
give Access an example of the information you wish
to see when you run your query.
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Create, run, and save queries
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 From the fields list, either drag or double-click fields
that you want included in the query.
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A query result differs from a table's datasheet view in
that only selected fields are displayed
 If you move a field to the design grid and then you
want to remove it, you can click on the field's column
and then press the delete key.
 The results of the query will be displayed in order by
the primary key of the table unless you specify
another sort order.
 You can save the query and give it a name by
pressing the save button on the toolbar.
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Update data using a query
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 You can use the query datasheet to update data in a
table.
 It is important to realize that the query datasheet
is a temporary view of the data.
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However, when you update data by means of the query
datasheet, the updates are placed directly into the
underlying table.
 You can only update fields that are represented in the
query.
 To observe the actual changes made to the table,
close the query and open the table in datasheet view.
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Access is a relational database
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 A database is almost always a collection of tables.
Access is a relational database management system
that allows you to form relationships between the
tables.
 When you form a relationship between tables, you
are joining the tables.
 Tables are joined on common fields between the
tables.
 When tables are joined, you can view data from both
tables as if the tables were one combined table.
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A one-to-many relationship
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 Tables can be joined in three ways; one-to-one, one-
to-many, and many-to-many.
 A one-to-many relationship exists when one table has
many records associated with a given value but the
related table has only one record for that value.
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The table with one record is called the primary table
The table with many records is called the related table
 Queries can be defined to use the relationship to
extract data from both tables in a single query.
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An example of a
one-to-many relationship
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The Employer table is related to the Position table via the common field EmployerID.
The Employer table has
one record for EmployerID
value 10126. The Position
table has two records.
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Query results for a
one-to-many relationship
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Queries can be built and saved that extract data from both
the primary table (Employer) and the related table (Position).
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Using referential integrity
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 Referential integrity allows you to maintain
the integrity between related tables.
 Referential integrity:
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when you add a record to a related table,
there must be a matching record in the
primary table.
 Enforcing referential integrity:
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insures no orphaned records (records that
have no matching record in the primary table).
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Cascaded Updates
and Cascaded Deletes
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 Cascaded updates:
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change in a field that is common to two related
tables will also cause change in the other table
 Cascaded deletes is similar.
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If you delete a field that is common to two
tables, the deletion will take place in both
tables.
 Be careful with these features, as they can
have dramatic effects on your data.
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Sort data in a query
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 You can control the order of data displayed in a query
by altering the queries sort key.
 Choose a field on which you want the data to be
sorted and then specify whether you want the data
sorted in ascending or descending order.
 Specify multiple fields as the sort key if you want to
arrange data in sorted order within groups of data.
 Specify sort criteria for the query in the query design
grid.
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Sort single or multiple fields
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To sort only one field, click in the desired field to select it, and then click the Sort
Ascending or Sort Descending button on the toolbar. To sort multiple fields, you must
specify them in the query design grid.
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Specify an exact match
condition in a query
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 You can specify an exact match condition, which
allows you to specify that only records that match
your criteria will be displayed.
 To specify an exact match, use the criteria row in
your query design grid.
 When you run the query after specifying an exact
match, only those records that meet the criteria will
be displayed.
 An exact match condition specifies that the value in
the specified field must match the condition exactly.
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Comparison Operators
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Use the And and Or logical
operators
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 When you need to use multiple conditions for a
query, you can use the logical operators to combine
conditions.
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The And logical operator specifies that both conditions
must be met
The Or logical operator specifies that one or the other
of the conditions must be met
 When you enter two conditions on the same row of
the query design grid, an And condition is created.
 If you enter two conditions that are on separate rows,
an Or condition is created.
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Illustration of And and Or logic
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The And
condition.
The Or
condition.
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Creating And and Or conditions
in the design grid
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And conditions must be
specified on the same line.
Or conditions must be specified on different lines.
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