1 Microsoft Access 2002 Tutorial 3 – Querying a Database

XP 2 The Query Window in Design View The Query window in Design view allows you to … 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.

XP 3 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. 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.

XP 4 Create, run, and save queries From the fields list, either drag or double-click fields that you want included in the query. 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.

XP 5 Update data using a query 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. 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.

XP 6 Access is a relational database 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.

XP 7 A one-to-many relationship 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. 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.

XP 8 An example of a one-to-many relationship The Employer table is related to the Position table via the common field EmployerID. The Employer table has one record for EmployerID value The Position table has two records.

XP 9 Query results for a one-to-many relationship Queries can be built and saved that extract data from both the primary table (Employer) and the related table (Position).

XP 10 Using referential integrity Referential integrity allows you to maintain the integrity between related tables. Referential integrity: when you add a record to a related table, there must be a matching record in the primary table. Enforcing referential integrity: insures no orphaned records (records that have no matching record in the primary table).

XP 11 Cascaded Updates and Cascaded Deletes Cascaded updates: change in a field that is common to two related tables will also cause change in the other table Cascaded deletes is similar. 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.

XP 12 Sort data in a query 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.

XP 13 Sort single or multiple fields 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.

XP 14 Specify an exact match condition in a query 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.

XP 15 Comparison Operators

XP 16 Use the And and Or logical operators When you need to use multiple conditions for a query, you can use the logical operators to combine conditions. 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.

XP 17 Illustration of And and Or logic The And condition. The Or condition.

XP 18 Creating And and Or conditions in the design grid And conditions must be specified on the same line. Or conditions must be specified on different lines.