Microsoft Access – Tutorial 3Querying a Databasea query is a question you ask about data stored in a

databaseyou tell Access what fields you need and what criteria

Access should use to select the recordsex. find records for employers located in a specific State or Province

queries allow you to: display selected fields and records from a table sort records perform calculations generate data for forms, reports and other queries update data in the tables in a database find and display data from two or more tables

Microsoft Access – Tutorial 3Query by Example (QBE)We use the Query Window in Design View to create a queryYou Query by Example by giving Access an example of the

information we are requestingAccess then retrieves the information we are requestingWe want to create a query to display:

employer ID employer name city contact first name contact last name web site information

for each record in the Employer table

Microsoft Access – Tutorial 3Query by Example (QBE)open the Northeast database we created last week

(I have included a copy in the Common Directory on the desktop)

Click Queries in the Objects barclick the New buttonmake sure Design View is selected and click OKshow the Employer Table and the close the Show Table

dialog boxmaximize the Select Query window

Microsoft Access – Tutorial 3Query by Example (QBE)you will see the field list in a box entitled Employer (the

table name)you can double-click or drag fields to the design grid in the design grid, you include the fields and record selection

criteria for the information that you want to seeyou can see the current results of your query at any time by

View button or the Run button on the Query Design toolbar

the current results will appear in a datasheet view

Microsoft Access – Tutorial 3Query by Example (QBE)drag the split bar and resize the windows as you likedouble-click the following fields in order: EmployerID,

EmpoyerName, City, ContactFirstName, ContactLastName and Website

note the checkbox that that allows you to show or hide fieldsclick Run (or View (Datasheet View)) to see the results in a

datasheetclick the View button to return to Design Viewclick the Save button on the toolbar and name the query

EmployerAnalysis

Microsoft Access – Tutorial 3Updating Data using a Query return to the Datasheet view indicate that The Adele Bannister House (10135) now has a

websitechange the Contact person for Alpine Touring Center

(10152) to Mary Grantclose the Query and note that it has been added to the

Queries in the Objects baropen the Employers table and verify that the changes have

been madeclose the Employers table

Microsoft Access – Tutorial 3Table Relationships remember that Access is a relational database management

system relationships are created among tables by using common

fields this process is often called a joinwhen you join tables with a common field, you can extract

data from them as if they were one table the Employer and Position tables are joined with the

common field EmployerID (a foreign key)you can use a query form or report to extract selected data

from each table even though the information is in two tables

Microsoft Access – Tutorial 3One-to-Many Relationshipsa one-to-many relationship exists between two tables when

one record in the first table matches zero, one or many records in the related table

and when one record in the in the second table matches exactly one record in the first table

the primary table is the one table in the one-to-many relationship this is the Employer table

the related table is the many table this is the Position table

Microsoft Access – Tutorial 3One-to-Many Relationshipsorphaned records can be created when inconsistencies

occur between tables for example:

if an Employer ID is changed in the Employer table if an Employer is deleted from the Employer table if a position is added for an Employer that doesn’t exist in the

Employer table

Microsoft Access – Tutorial 3One-to-Many RelationshipsReferential Integrity is a set of rules that Access uses to

prevent records from being orphaned it maintains consistency between tables when you update

data when you add a record to a related table, a matching record

must already exist in the primary table if you attempt to change the value of a primary key in the

primary table, Access prevents the change if matching records exist in a related table (however, if the cascade updates option is chosen, the foreing key values will be updated automatically)

Access prevents the deletion of records in a primary table if matching records exist in a related table(if cascade deletes option is selected all records with that key will be deleted – this is not recommended)

Microsoft Access – Tutorial 3Defining Relationshipsyou can define relationships between tables using the

Relationships windowclick the Relationships button on the Database toolbaradd Employer and AvailablePositions and close the Show

Table dialog box lengthen and widen each window to show all fieldsclick and drag EmployerID from the Employer Table to

EmployerID in the AvailablePositions table the Edit Relationships window will appear the Primary Table, Related Table and Common Field will be

visible

Microsoft Access – Tutorial 3Defining Relationshipscheck Enforce Referential Integritynote that the two Cascade options become availablecheck Cascade Update Related Fields

(remember that it is not recommended to check the Cascade Delete Related Records as you may inadvertently delete records)

click create and note the join line that appears and the symbols on it

now create a one-to-many relationship between the NAICS table and Employer Table with NAICS code as the common field (foreign key)

click the Save button and Close the window

Microsoft Access – Tutorial 3Multi-Table Queriesnow that we have created Relationships among (joined) our

tables, we can query them as onecreate a new query in design viewadd the Employer and PositionsAvailable tablescreate a query in the following order:

EmployerName City StateProv Openings PositionTitle StartDate EndDate

run it and save the query as EmployerPositions

Microsoft Access – Tutorial 3Sorting Data in a Querysorting is rearranging records in a specified order or

sequenceopen the EmployerPositions query in datasheet viewselect the first record in the Employer Name field and use

the sort buttons to sort alphabetically to sort by more than one field go to Design Viewselect the entire column for Openingsclick and drag it so that it is the last field (after EndDate)use the Sort field to sort PositionTitle Ascending sort Openings Descending run the querywithin groups of fields with the same Position Title, the

record – save the query

Microsoft Access – Tutorial 3Filtering Data in a Queryyou can filter query results using the Filter by Selection

buttondouble-click the word clerk in one of the Position Title

recordsclick the Filter by Selection button and you will see only

results for different kinds of clerksclick the remove filter button to turn off the filter filter results for New Hampshire (NH)

Microsoft Access – Tutorial 3Defining Record Selection Criteriayou can specify a condition which is a criteria or rule that

tells Access which records to displaywe will create query by using wizard using a conditionclick create query by using wizard and make sure the

Table: AvailablePositions is selectedadd all the fields by clicking >> remove both PositionID and EmployerID from the Selected

Fields list box to add fields from another table after the current set of fields,

select Openingsnow add EmployerName, StateProv, ContactFirstName,

ContactLastName and Phone from the Employer Table

Microsoft Access – Tutorial 3Defining Record Selection Criteriaclick the Next buttonmake sure the Detail radio button is selected and click Next

againname the Query July1Positions and click the Modify the

Query Design radio button in the StartDate Criteria type 07/01/2006Access adds # signs before and after the criteria run and save the queryonly positions with start dates of July 1st will be displayed

Microsoft Access – Tutorial 3Formatting the Appearance of the sheetselect all the recordsFormat>Fontchange the size of the fonts to 8double click between columns to resize them

Microsoft Access – Tutorial 3Setting Range Criteriaopen the July1Positions query in Design View remove the Start Date criteriaset the Wage criteria >=17 run the query and Save it As HighWageAmounts

Microsoft Access – Tutorial 3Using Multiple Selection Criteria with the And operatoropen the July1Positions query in Design Viewadd PE as criteria for StateProv run the Query and you’ll see results that match both criteriaclose and save the query right click on the Query July1Positions in the Query window rename it PEJuly1Positions

Microsoft Access – Tutorial 3Using Multiple Selection Criteria with the Or operatorcreate a new query in Design viewuse the Employer and AvailablePositions tables and add the

following fields: EmployerName, City, PositionTitle, HoursPerWeek, and Experience

set the HoursPerWeek criteria to <30 in order to select records in which either (not both) of the

conditions is met type Yes in the or: field run the querysort it alphabetically ascending by Employer NameSave it as HoursorExperience