Web-Enabled Decision Support Systems

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Transcript Web-Enabled Decision Support Systems

Web-Enabled Decision Support Systems Queries: Building Application Foundation

Prof. Name Position University Name 1 [email protected]

(123) 456-7890

Overview

              

8.1 Introduction

8.2 Working with Select Queries 8.3 Queries with Multiple Tables (The Join Operation) 8.4 Working with Operators 8.5 Hands-On Tutorial: A Select Query with Join of Multiple Tables 8.6 Using Total Row (The GroupBy Operation) 8.7 Creating Calculated Fields 8.8 Parameter Queries 8.9 Crosstab Queries 8.10 Action Queries 8.11 Update Queries 8.12 Delete Queries 8.13 Append Queries 8.14 In-Class Assignment 8.15 Summary 2

Introduction

 A database

query

is a question posed against database tables – A set of instructions – Enable us to present a

unified view of data

 From single or multiple tables – When executed, operate on database tables to output the

query result

  Single Number (aggregate query) Record Set (select query)  Built using: – Graphical query design grid (Query By Example, QBE) – Standard Query Language (SQL) statements 3

Introduction

(Cont.)  Access queries can be broadly classified into three function-based categories: – Select queries – Special purpose queries (Crosstab, Parameter, and Make-Table queries) – Action queries (Update, Append, and Delete queries) The Access Query Menu 4

Overview

               8.1 Introduction

8.2 Working with Select Queries

8.3 Queries with Multiple Tables (The Join Operation) 8.4 Working with Operators 8.5 Hands-On Tutorial: A Select Query with Join of Multiple Tables 8.6 Using Total Row (The GroupBy Operation) 8.7 Creating Calculated Fields 8.8 Parameter Queries 8.9 Crosstab Queries 8.10 Action Queries 8.11 Update Queries 8.12 Delete Queries 8.13 Append Queries 8.14 In-Class Assignment 8.15 Summary 5

Working With Select Queries

 Select Queries – Most common type of query used in database applications – Extract and output recordsets that satisfy specific selection criteria:  Arithmetic expressions  Logical expressions – Composed of three types of operations:    Projection operations Selection operations Sorting operations 6

Projection



Projection

is a vertical slicing of an input recordset – Used to display one or more selected fields of a table – Example:  Input recordset:

Student

table  Output recordset:

Name

Email

, and

DOB

fields The Projection Operation 7

Selection



Selection

is a horizontal slicing of an input recordset – Used to select one or more records (rows) that satisfy specified selection criteria – Example:   Input recordset:

Student

table Selection criteria:

Type

= “Full Time” The Selection Operation 8

Sorting



Sorting

provides an ordered sequence of an input recordset – Example:   Input recordset:

Student

table Sort:

StudentID

(ascending) The Sorting Operation 9

Creating a Query in the Design View

 The

Design View

and

Simple Query Wizard

are the two most frequently used options for creating queries  How-to: Create a New Query Using Design View 1. Select the

Queries

option in the Objects Bar to display the two popular options for creating a new query.

“Create Query” Options 10

Creating a Query in the Design View

(cont.) 2. Double-click on the

Create query in Design View

option to open a new query in the Design View.

New Query

Dialog Box 11

Query Design View

 The

Query Design View

is divided into two halves: – The upper half, called a

Table Pane

, displays all the fields from the desired query tables – The lower half, the

Design Grid

, holds the table fields on which we would like perform Projection, Selection, and/or Sorting operations The Query Design View 12

A Select Query Example

 Query: – “List the students’ information (

StudentID

Name

, and

Email

) for all full time, freshman students sorted in descending order of their names.”  Steps: 1. Projecting student identification number, name, and email columns 2. Selecting only full time, freshman students 3. Sorting selected records in descending order of student names 13

Projecting Student’s Contact Information

 How-to: Build a Select Query 1. Open the university database and create a new query in the Design View.

2. Select the table

tblStudent

design. and click the

Add

button to add it to the query 3. Click

Close

to exit the

Show Table

dialog box. 4. Add the

StudentID

Name

, and

Email

fields to the Design Grid. Projecting Fields of the Student Table 14

Saving and Executing a Query

 How-to: Build a Select Query (cont.) 5.

Save this query as “QrySelection” and run the query to verify the Projection operation.  To save, choose

File

Save

from the Main menu.

 To run, choose

Query

Run

from the Main menu.

Selecting Freshman and Fulltime Students

 How-to: Build a Select Query (cont.) 6.

Add =“Freshman” criterion for the

Class

column and =“Full Time” criterion for the

Type

column in the

Criteria

row.

7. Uncheck the check boxes in the

Show

columns. row for the

Class

and

Type

8. Save and run the query to verify Selection operation.

Selecting Rows of the Student Table 16

Sorting Student’s Records

 By default, query results are displayed in the same order in which they appear in the table  How-to: Build a Select Query (cont.) 9.

Choose the “Descending” order using the drop-down list in the

Sort

row of the

Name

column.

Sorting Student Records in Descending Order by Student Names 17

Query Output

 How-to: Build a Select Query (cont.) 10. Save and run the query to verify Selection operation.

Output of the Example Select Query 18

Moving or Removing Fields and Tables in Design View

 By default, the order of the columns in the Design Grid is the order of the columns in the query result  Moving columns in the Design Grid: – Select the entire column and drag it to the desired location.  Removing columns from the Design Grid: – Select the entire column and hit the

Delete

button.

 Removing tables from the Table Pane: – Select the table by clicking on the table list and then remove it by hitting the

Delete

button.

– Removes the corresponding columns of that table from the Design Grid. 19

Exploring Query Toolbar and Menus

Picture Name

Design View Query Type Show Table

Functionality

Switches to the Design View Provides options to choose query type Opens the

Show Table

dialog box to add tables/queries

Main Menu

View | Design View Query | {Query Type Name} Query | Show Table Totals Properties Adds

Total

row to the Design Grid for total queries View | Totals Opens the

Query Properties

window View | Properties Build Opens the

Expression Builder

dialog box -

Short-cut Menu

Table Pane | Design View Table Pane | Query Type | {Query Type Name} Table Pane | Show Table

Criteria

- Design Grid | Properties row | Build 20

Overview

               8.1 Introduction 8.2 Working with Select Queries

8.3 Queries with Multiple Tables (The Join Operation)

8.4 Working with Operators 8.5 Hands-On Tutorial: A Select Query with Join of Multiple Tables 8.6 Using Total Row (The GroupBy Operation) 8.7 Creating Calculated Fields 8.8 Parameter Queries 8.9 Crosstab Queries 8.10 Action Queries 8.11 Update Queries 8.12 Delete Queries 8.13 Append Queries 8.14 In-Class Assignment 8.15 Summary 21

Queries with Multiple Tables (The Join Operation)

  Queries can systematically join multiple tables to create a unified view of the fragmented data

Join operations

involve adding multiple tables to the Table Pane – Combine with projection, selection, and sorting operations to create more complex queries The Join Operation 22

Hands-On Tutorial: Working with Join Queries

  Query: – “List the student information (

StudentID

departments (not the

DeptID

).” and

Name

) and name of their How-to: Design a Query that Involves Multiple Tables 1. Open the university database and start with a new query in the Design View. Add the

tblStudent

and

tblDepartment

to the Table Pane.

2. Add the required fields to the Design Grid. Joining Student and Department Tables in the Design View 23

Hands-On Tutorial: Working with Join Queries

(cont.) 3.

Save the query as “QryJoinQuery” and run it. The Join Result in the Datasheet View 24

The Join Operation

 The

join operation

takes two distinct recordsets as an input and produces a single output recordset, referred as the

join result

– Each record from the first recordset is joined with all records in the second – The join result filters these joined records via the

join condition

 An

inner join

is based on an equality condition of primary key-foreign key columns – Default join type – Join results will include records from both the tables which satisfy the primary key-foreign key conditions – When adding related tables to the Table Pane, Access automatically displays such relationships 25

The Join Operation

(cont.) 

Outer joins

include all the records from one table and only those records from the other table where joined fields are equal –

Left outer joins

include all records in the left table  Default outer join type –

Right outer joins

include all records in the right table  If the two tables added to the Table Pane to join are not related to each other, no join condition is used in the join operation – Join result in an

all-to-all join

(or

Cartesian product join

) – Each record from the first input recordset is joined with all the records from the second input recordset 26

Join Properties

 We can view and alter join types using the

Join Properties

dialog box – To invoke the

Join Properties

dialog box, right-click the relationship line in the Table Pane and choose

Properties

from the short-cut menu. Selecting a Join Type in

Join Properties

Dialog Box 27

Overview

               8.1 Introduction 8.2 Working with Select Queries 8.3 Queries with Multiple Tables (The Join Operation)

8.4 Working with Operators

8.5 Hands-On Tutorial: A Select Query with Join of Multiple Tables 8.6 Using Total Row (The GroupBy Operation) 8.7 Creating Calculated Fields 8.8 Parameter Queries 8.9 Crosstab Queries 8.10 Action Queries 8.11 Update Queries 8.12 Delete Queries 8.13 Append Queries 8.14 In-Class Assignment 8.15 Summary 28

Working with Operators

 In Access, we have an option to use different operators in the query design to build conditional statements  Most commonly used operators: – Comparison operators – Logical operators – BETWEEN operator – LIKE operator 29

Comparison Operators

 We use

comparison operators

to select a specific group of records from a table – Operators:  >, >=, <, <=, =, !=  Examples: –

CreditHours

> 3.0

–

Year

= 2002 30

The Logical Conditions

 We need

logical operators

to combine multiple criteria – Operators:  AND, OR, and NOT  Examples: – – –

Salary

> 7000 AND

Salary

< 10000

Class

= “Sophomore” OR

Class

= “Freshman”

Class

= “Sophomore” AND

Type

= “Full Time” 31

The BETWEEN Operator

 We use the

BETWEEN operator

along with the logical AND operator to specify an inclusive range between two values – For use with text, numeric, or date fields  Examples: – BETWEEN #1/1/95# AND #1/1/2002# – BETWEEN 70,000 AND 100,000 32

The LIKE Operator and Wildcard Character

  The

LIKE operator

finds groups of potentially related items It is often used with the

wildcard character

, the asterisk (*)  Examples: – LIKE “*Computer*”  Text includes “Computer” – LIKE “Applied*”  Text begins with “Applied” 33

Working with Dates

  We use the pound sign (#) to represent the date data type Access has many built-in functions to handle dates and times data types  Example: – <= #1/1/2001#  Everything on and before January 1, 2001 – < Now()  Everything before current date 34

Overview

               8.1 Introduction 8.2 Working with Select Queries 8.3 Queries with Multiple Tables (The Join Operation) 8.4 Working with Operators

8.5 Hands-On Tutorial: A Select Query with Join of Multiple Tables

8.6 Using Total Row (The GroupBy Operation) 8.7 Creating Calculated Fields 8.8 Parameter Queries 8.9 Crosstab Queries 8.10 Action Queries 8.11 Update Queries 8.12 Delete Queries 8.13 Append Queries 8.14 In-Class Assignment 8.15 Summary 35

Hands-On Tutorial: A Select Query with Join of Multiple Tables

 Query: – “List the contact information (

name

email

, and

address

) for all Industrial Engineering (ISE) students who have taken any computer- or database related courses in the last six years and earned a grade point average of 3.5 or better in these courses. Sort the list in descending order of student’s letter grade.”  Tables: – Student table – Transcript table – Section table – Course table 36

Hands-On Tutorial

(cont.)

: A Select Query with Join of Multiple Tables

 How-to: Write a Complex Query using the Projection, Selection, Sorting, and Join Operations 1. Open the university database and start with a new query in the Design View. Add the required four tables to the Table Pane. 2. Add the required fields from their respective tables to the Design Grid. A Select Query Design with Multiple Tables 37

Hands-On Tutorial

(cont.)

: A Select Query with Join of Multiple Tables

3. Add the criteria >= 3.5 for the

Grade

=“ISE” for the

DeptID

field.  column. Specify the expression Save and run the query to verify the design so far.

4. Assign the expression > Year (Now ()) - 6 in the

Year

field. A Select Query Design with Multiple Tables 38

Hands-On Tutorial

(cont.)

: A Select Query with Join of Multiple Tables

Place the final expression Like “*computer*” Or Like “*database*” in the course name field. 6. Use the

Sort

row to specify descending order for the

Grade

column. 7. Use the

Show

row to display only the

Name

Address

, and

Email

columns. Uncheck all other columns in the

Show

row.

8. Save and run the query. 39

Overview

8.6 Using Total Row (The GroupBy Operation)

8.7 Creating Calculated Fields 8.8 Parameter Queries 8.9 Crosstab Queries 8.10 Action Queries 8.11 Update Queries 8.12 Delete Queries 8.13 Append Queries 8.14 In-Class Assignment 8.15 Summary 40

Using Total Row (The GroupBy Operation)

 The

GroupBy operation

puts together records based on some similarity criteria and treats them as one unit or a group – Extensively used to furnish data summaries – Allows us to apply aggregate functions to the set of records 41

Hands-On Tutorial: Using the Total Row

 Query: – “Determine the total number of students in each department.”  How-to: Create a

Totals

(or GroupBy) Query 1. Open the university database and start with a new query in the Design View. Add the student and department tables. 2. Add the student ID and department name fields to the Design Grid. 3. Designate this query as a

Totals

the toolbar. query by clicking on the

Totals

button on 4. Click in the

Total

row under the

StudentID

column, and select the

Count

option from the drop-down list of aggregate functions.

Hands-On Tutorial: Using the Total Row

(cont.) 5. The Design View should appear as below: Grouping Student Records by Department in the Design View 43

Hands-On Tutorial: Using the Total Row

(cont.) 6. Save and run the query for the result shown below.

 Aggregation fields (like

StudentID

in this example) are named as

Of.

7. Rename the

StudentID

count column as “

TotalStudents: StudentID

”.

The Output of GroupBy Operation 44

Hands-On Tutorial: Using the Total Row with the Where Clause

 Query: – “List the course information for those courses whose average evaluation was better than 80 points in the last 5 years.”  How-to: Create a

Total

Query Using the

Where

Clause in the

Total

Row 1. Open the university database and start with a new query in the Design View. Add the course and section tables. 2. Add the

Name

field from the course table and the fields from the section table to the Design Grid.

Evaluation

and

Year

3. Designate this query as a

Total

query by clicking on the

Totals

the toolbar. button on 45

Hands-On Tutorial

(cont.)

: Using the Total Row with the Where Clause

4. Click on the

Total

row under the

Evaluation

column, and select the

Average

option from the drop-down list of aggregate functions. 5. Add selection criteria (> Year (Now ()) - 5) using the

Where

option under the

Year

column. 6. Specify the selection criteria (>80) for the

Evaluation

column. 7. Remove the check in the 8.

Show

row for the

Year

column. Save the query as “QryCourseEvaluation” and run it. The Query Output 46

Hands-On Tutorial

(cont.)

: Using the Total Row with the Where Clause

– The final Design View is shown below:

The Total Row with the Where Clause

Overview

8.7 Creating Calculated Fields

8.8 Parameter Queries 8.9 Crosstab Queries 8.10 Action Queries 8.11 Update Queries 8.12 Delete Queries 8.13 Append Queries 8.14 In-Class Assignment 8.15 Summary 48

Creating Calculated Fields

 Access queries allow us to create

calculated fields

as a part of the query design – Used to represent derived attributes  Attributes that are calculated using other attributes of the relation – Expressed as a new field in separate column of the query Design Grid  Instead of adding a column from the Table Pane, we write an expression in the Design Grid that, when evaluated, gives the value of the field  Existing field names are enclosed in square brackets [ ] to distinguish them from other entries in the expression – Example:  Age: Now() – [DateOfBirth] 49

Hands-On Tutorial: Creating Calculated Fields

 Calculated Field: – Grade Point Average (GPA)  Calculated by first summing the product of the grade point and corresponding credit hours and then averaging it over the total number of credit hours earned  How-to: Create the Calculated Fields in Access Queries 1. Open the university database and start with a new query in the Design View. Add required tables to the Table Pane.

2. Add the student

Name

StudentID

, and

CreditHours

Grid. fields to the Design 3. Click the

Total

function in the button on the toolbar and select the

Total

row of the

CreditHours Sum

aggregate column. Rename this column as

TC:CreditHours.

Hands-On Tutorial: Creating Calculated Fields

(cont.) 4. Add the calculated field TG: [CreditHours]*[Grade]. Choose the

Sum

aggregate in the

Total

row.

5. Add another calculated field, GPA: [TG]/ [TC]. Assign an

Expression

option in the

Total

row for this column.

Creating Calculated Fields for GPA Calculations 51

Calculated Fields with Strings

 We can also perform string operations on fields  Example: – Name: [FirstName] & “ ” & [LastName]   Obtains the full name by combining the first name and the last name The ampersand (&) operator combines the string values from

FirstName

LastName

, and an empty string 52

Expression Builder

 The Access

Expression Builder

dialog box simplifies the process of developing complicated expressions for calculated fields – To invoke the

Expression Builder

dialog box, click the

Build

button on the toolbar.

The Expression Builder Dialog Box

Overview

8.8 Parameter Queries

8.9 Crosstab Queries 8.10 Action Queries 8.11 Update Queries 8.12 Delete Queries 8.13 Append Queries 8.14 In-Class Assignment 8.15 Summary 54

Parameter Queries

 A

Parameter query

is a query that prompts for parameter values and dynamically assigns user-entered values in the selection criteria to run the query – At each execution, users may enter different parameter values for the desired result  We create a Parameter query in the same manner we create a Select query – We specify one or more parameters of the query in the selection criteria using square brackets [ ]  DeptID = [ ] – To prompt the user with an appropriate message to enter parameter values, enclose the message in the square brackets  DeptID = [Please Enter Department Name] 55

Parameter Queries

(cont.) The Parameter Query in the Design View 56 The Query Output

Hands-On Tutorial: Working with Parameter Queries

 Query: – “Display a list of faculty members who have joined a particular college within a specified date range.”  Tables: – – –

tblCollege tblDepartment tblFaculty

Hands-On Tutorial: Working with Parameter Queries

(cont.)  How-to: Work with the Parameter Queries 1. Open the university database for a new query in the Design View. Add the college, department, and faculty tables to the Table Pane.

2. Add fields to the Design Grid as shown below. The Parameter Query with Multiple Parameters 58

Hands-On Tutorial: Working with Parameter Queries

(cont.) 3.

Enter the “[Enter the College]” parameter for the

CollegeID

column. Also, assign the “Between [Starting Date] And [Ending Date]” criteria under the

JoiningDate

column. 4. Save and run the query. The Parameter Query with Multiple Parameters 59

Overview

               8.1 Introduction 8.2 Working with Select Queries 8.3 Queries with Multiple Tables (The Join Operation) 8.4 Working with Operators 8.5 Hands-On Tutorial: A Select Query with Join of Multiple Tables 8.6 Using Total Row (The GroupBy Operation) 8.7 Creating Calculated Fields 8.8 Parameter Queries

8.9 Crosstab Queries

8.10 Action Queries 8.11 Update Queries 8.12 Delete Queries 8.13 Append Queries 8.14 In-Class Assignment 8.15 Summary 60

Crosstab Queries



Crosstab queries

are used to group and summarize the information and display it in a spreadsheet format – Less repetition of information than in the Datasheet View – Easier to read and analyze  Crosstab queries are defined by three fields: – Row-heading fields:

DeptID

– Column-heading fields:

Class

(one column for each distinct Class) – Value fields:

StudentID

Output of a Crosstab Query 61

Hands-On Tutorial: Working with Crosstab Queries

 Query: – “For all the courses in the Computer Science department, we would like to display the total student enrollment in the Fall, Spring, and Summer semesters.”  Fields: – Row-heading fields:

Course Names

– Column-heading fields:

Sem

– Value fields:

StudentID

Hands-On Tutorial: Working with Crosstab Queries

(cont.)  How-to: Work with Crosstab Queries 1. Open the university database with the new query, and add the course, section, and transcript tables to the Table Pane.

2. Add the

CourseID

Name

, and

DeptID

fields from the course table, the

StudentID

field from the transcript table, and the section table.

Sem

field from the 3. Change the type of query from the default Select query to the Crosstab query by choosing the

Query

Crosstab Query

item from the Main menu. 4. Select the

Row Heading

option for the

CourseID

and

Name

columns in the

Crosstab

row. 63

Hands-On Tutorial: Working with Crosstab Queries

(cont.) 5. Select the

Column Heading

option for the

Sem

field. 6. Select the

Value

option for the

StudentID

function in the

Total

row for the

StudentID

field. Also choose the

Count

column. 7.

Specify the department selection criteria (=“CISE”) under

DeptID

column. The Crosstab Query (Students per Semester per Course) in the Design View 64

Hands-On Tutorial: Working with Crosstab Queries

(cont.) 8. Save and then run the query to produce the result shown: The Output of the Crosstab Query (Students per Semester per Course) 65

Overview

8.10 Action Queries

8.11 Update Queries 8.12 Delete Queries 8.13 Append Queries 8.14 In-Class Assignment 8.15 Summary 66

Action Queries

 Queries that can alter data by performing actions are called

action queries

– Allow us to modify a large number of records without having to write any special programs – Does not return a recordset – Three Types: 

Update queries

modify the values of one or more fields in the table 

Delete queries

use criteria to delete one or more records from the table 

Append queries

append one or more records to an existing table 67

Overview

8.11 Update Queries

8.12 Delete Queries 8.13 Append Queries 8.14 In-Class Assignment 8.15 Summary 68

Update Queries

 An

update query

is an action query that can change field values in an existing table – Primarily update existing values in the database fields – Example:  Increase the

Salary

field of the faculty table by 5% Faculty Table Before 69 Faculty Table After

Update Queries

(cont.)  We can select the records we would like to update by specifying update criteria – Example:  “Raise the salary for faculty members who joined the university before 1995 and have a salary of less than $70,000.” The Update Query in the Design View 70

Hands-On Tutorial: Working with an Update Query

 Query: – “Update the

Salary

field in the faculty table for those faculty members who joined the university before 1995 and have a salary less than $70,000.”  How-to: Work with Update Queries 1. Open the university database and begin with a new query in the Design View. Add the faculty table to the query design.

2. Change the query type to the Update query. 3. Add the

Salary

and

JoiningDate

Grid. In the

Salary

fields from the table list to the Design field, enter the expression [Salary]*1.05 under the

Update To

row.

Hands-On Tutorial: Working with an Update Query

(cont.) 4. In the

JoiningDate

the

Salary

field, specify the following criteria: “< #1/1/1995#”. In field, enter the criteria: “< 70,000”.

Save the query as “QrySalaryUpdates” and run it using the

Run

button on the toolbar. Click

Yes

when Access flashes a warning message.

Access’ Update Warning 72

How to Preview Records that the Action Query Alters

 When we run action queries, the changes made to the database tables are irreversible – It is important that we preview the exact changes that will occur  To preview, click the

View

button on the toolbar at the top left corner of the Database Window.  This opens a Datasheet View with records that the action query will alter. Preview of an Update Query in the Datasheet View 73

How Cascade Updates Work with Update Queries

 What happens when we update the primary key of a table that is a foreign key in some other table and vice versa? – Update primary key:   Access allows us to update the primary key value If the

Cascade Updates

option is selected, then Access automatically updates the foreign key value to maintain referential integrity – Update foreign key:  Access warns us for referential integrality constraint violations  If we continue with this update, we leave data in an inconsistent state The Cascade Update Error 74

Overview

8.12 Delete Queries

8.13 Append Queries 8.14 In-Class Assignment 8.15 Summary 75

Delete Queries

 A

delete query

is an action query that deletes records from existing tables – Allow us to delete specific groups of records by applying deletion criteria to the appropriate fields The Delete Query in the Design View 76 Preview of the Delete Query Displaying Records to be Deleted

Hands-On Tutorial: Building a Delete Query

 Query: – “Delete the Industrial Engineering student records for those students who have recently graduated (i.e., say all of the senior class).”  How-to: Work with Delete Queries 1. Open the university database and start with the new query in the Design View. Add the student and department tables to the query design.

2. Change the query type from the default Select query to the Delete query. 3. Add the

Class

and

DeptID

fields from the student and department lists, respectively, to the Design Grid. 77

Hands-On Tutorial: Building a Delete Query

(cont.) 4. Add all fields from the student tables by adding an asterisk (*) to the Design Grid. 5. Specify the criteria fields for

Class

as = “Senior” and for

DeptID

as = “ISE”. 6.

Save the query as “qryDelStudents”. Preview the deleted records using the

View

button on the toolbar.

The Delete Query in the Design View 78

Caution with Cascade Delete Option

 Access performs cascade deletes when the delete query removes records that contain primary key values – Cascade deletes often increase the danger of massive data loss – Should be used with caution 79

Append Queries

8.13 Append Queries

8.14 In-Class Assignment 8.15 Summary 80

Append Queries

 An

append query

is an action query that copies records from one or more tables and adds them at the end of another table – Example:  “Retrieve the contact information and the date of birth of students in the College of Engineering and append them to a temporary table in the database for further processing.” Append Query in the Design View 81 Preview of the Append Query

Hands-On Tutorial: Building an Append Query

  Query: – “Select the contact information and birthdates for all students in the College of Engineering and append them to a temporary table,

tblStudentArchive

, in the database for further processing.” How-to: Work with Append Queries 1. Start with a new query and add the student, department, and college tables to the query design. 2. Change the query type to the Append query to display the

Append

dialog box. Select the

tblStudentArchive

table from the drop-down list. The

Append

Dialog Box 82

Hands-On Tutorial: Building an Append Query

(cont.) 3. Add all the required fields and the selection criteria as shown below. 4.

Save the query as “QryStudentArchive”. Preview the records selected to append to the archive table and run the query. Append Query in the Design View 83

Overview

8.14 In-Class Assignment

8.15 Summary 84

In-Class Assignment

 Consider the

Bottling.mdb

database, the database of a soft drink bottling plant. – The database manager has observed several defects in production. – The quality expert wants to investigate whether there is a relationship between bottle characteristics (such as material and size) and the number of defects. 1. Create a query that, for each type of material and bottle size, calculates the sum of the fraction of nonconforming bottles (the fraction is the ratio of the number of defective bottles to the total number of bottles). Title the query, “QryMaterials”. Are there any trends?

2. Create a query that, for each type of drink, displays the sum of the fraction of nonconforming bottles. Title the query, “QryDrinkType”. Are there any trends?

Overview

8.15 Summary

Summary

 A

query

is a question posed against database tables.

 Access allows us to build queries using a graphical query grid (Query by-Example or QBE) and by writing SQL statements.

 Access queries can be broadly classified into three function-based categories: – Select Queries – Special Purpose Queries (Crosstab, Parameter, and Make-Table queries) – Action Queries (Update, Append, and Delete queries) 

Select queries

applications. are the most common type of query used in database – A Select query selects or extracts data from one or more existing tables and displays the selection in the Datasheet View.

Summary

(cont.)  Query Operations

–

Projection

is a vertical slicing of a recordset. – –

Selection

is a horizontal slicing of a recordset.

Sorting

provides an ordered sequence of a recordset. –

Join

is a vertical merging of two tables. – The

GroupBy

operation places similar records together and treats them as one unit or group.  A

parameter query

prompts user for criteria values when the query is executed. – The input values are then used in the selection criteria to run the query.

 We use

crosstab queries

to group and summarize information and display it in a spreadsheet format. – Create less repetition of information in the datasheet, making it easier to read and analyze the selected field data.

Summary

(cont.)  Access queries are not restricted to data retrieval  Queries that can alter data by performing actions are aptly called

action queries

: – –

Update queries

modify the values of one or more fields in the table.

Delete queries

use criteria to delete one or more records from the table. –

Append queries

append one or more records to an existing table.

Additional Links

 Review more sample Access Queries from database files on the book website: http://www.dssbooks.com

 Refer

MS Access 2003: The Complete Reference

by Virginia Andersen for more details on Access Queries.

 Also refer

Access 2003 Bible

by Cary N. Prague, Michael R. Irwin, and Jennifer Reardon.

 Also see: http://msdn.microsoft.com/ for useful tips on Access Queries.