Using the Select Case Statement and the MsgBox Function

(Unit 8)Visual Basic for Applications

Objectives

In this unit, you will learn how to:

Perform selection using the Select Case statement

Use a message box to communicate with the user

Use the QueryTables collection and QueryTable object in Excel to retrieve external data

Use the SQL SELECT statement in Excel, Word, and Access to select records

Use the MailMerge object in Word to create labels

Concept Lesson:More on the Selection Structure

You might have more than two paths from which a selection structure must choose

When a selection structure has several paths from which to choose, it is usually simpler and clearer to use the Case form of the selection structure instead of the nested If form

The Case form is sometimes referred to as an extended selection structure in a procedure

The Select Case Statement

The Select Case statement begins with the Select Case clause and ends with the End Select clause

Between the Select Case and End Select clauses are the individual Case clauses

Each Case clause represents a different path that the selection structure can follow

The Select Case clause must include a testexpression

The testexpression can be any numeric, string, or Boolean expression

The Select Case Statement

Each of the individual Case clauses, except theCase Else, must contain an expressionlist, whichcan include one or more numeric, string, orBoolean expressions

The data type of the expressions included in the expressionlists must be compatible with the data type of the testexpression

When the Select Case statement is processed, the value of the testexpression is first compared with the values listed in expressionlist1

If a match is found, the instructions for the first Case clause are processed and then the instruction following the End Select clause is processed

Syntax and an Example of the Select Case Statement

Exhibit 8-1: The syntax and an example of the Select Case statement

Using To and Isin an Expressionlist

You can use either the keyword To or Is to specify a range of values in an expressionlist; the values included in the range can be either numeric or a string

When you use the To keyword in a Case clause, the value preceding the To always must be smaller than the value following the To

If you neglect to type the keyword Is in an expression, the Visual Basic Editor will type it in for you

Example of Using the To and IsKeywords in a Select Case Statement

Exhibit 8-3: An example of using the To and Is keywords in a Select Case statement

The MsgBox Function

In addition to the MsgBox statement, VBA also has a MsgBox function

The MsgBox function allows you to display a dialog box that contains a message, one or more command buttons, and an icon

After displaying the dialog box, both the MsgBox statement and the MsgBox function wait for the user to choose one of the command buttons

Unlike the MsgBox statement, the MsgBox function returns a value that indicates which button the user chose

Syntax and Examples of the MsgBox Statement & the MsgBox Function

Exhibit 8-4: The syntax and examples of the MsgBox statement and the Msgbox function

The Buttons Argument

The buttons argument is an optional numeric expression that represents the sum of values specifying the number and type of buttons to display in the dialog box, the icon style to use, and the identity of the default button

If you omit the buttons argument, the dialog box contains an OK button only; it does not containan icon

The buttons argument’s settings are divided into three groups

If you do not want to display an icon in the message box, you do not need to include a number from the second group in the buttons argument

Valid Settings for the buttons Argument

Exhibit 8-5: The valid settings for the buttons argument

MsgBox Function’s Buttons

Exhibit 8-6: The Msgbox function’s buttons

Values Returned by the MsgBox Function

If the user selects the Retry button, the MsgBox function returns the integer 4, represented by the intrinsic constant vbRetry

Exhibit 8-7: Some examples of using the Msgbox function’s return values

Summary

To use the Select Case statement to code the selection structure:

Use the syntax shown in Figure 8-1, where the testexpression and the expressionlists can contain a numeric, string, or Boolean expression composed of a combination of variables, constants, functions, and operators

To specify a range of values in a Case clause’s expressionlist:

Use the keyword To in the following syntax: smallest value in the range TO largest valuein the range

Summary

Use the keyword Is in the following syntax: Is relational operator value

To display VBA’s predefined message box, and then

return a value that indicates the button that was

selected in the message box:

Use the MsgBox function.

Excel Lesson:Viewing the MthSales Database

and the Sales Worksheet

The Student Data folder contains the Access database that is used to record each store’s monthly sales information

The databaseis named MthSales, andit is stored in the Tut08\Excel folder

Viewing the MthSales Database and the Sales Worksheet

To view the workbook:

1. Start Microsoft Excel

2. Open theT8-EX-1 (T8-EX-1.xls) workbook, which is located in the Tut08\Excel folder in the Student Data folder on your hard drive.

Click the Enable Macros button, if necessary, then save the workbook as Monthly Sales. The Monthly Sales workbook contains one worksheet, named Sales.

Using Microsoft Query

Microsoft Query is a separate program that comes with Microsoft Excel, and it is usedto bring data from a database into anExcel worksheet

Microsoft Query can retrieve data from the following database sources: Microsoft SQL, Microsoft Access, Microsoft Excel, Oracle, SQL Server, and text file databases

Remarks Using Microsoft Query

If you import data using the user interface, data from a Web query or a text query is imported as a QueryTable object, while all other external data is imported as a ListObject object.

If you import data using the object model, data from a Web query or a text query must be imported as a QueryTable, while all other external data can be imported as either a ListObject or a QueryTable.

http://msdn.microsoft.com/en-us/library/office/ff834459.aspx

The QueryTables Collection and QueryTable Objects

Each QueryTable object represents a worksheet table built from data retrieved from an external data source

You can use the QueryTable object’s CommandText property to select a different set of records to retrieve from the database and display in the worksheet

Exhibit 8-9: The QueryTables collection and QueryTable objects shown in the Excel Object Model

Create a Query Table in VBAPublic Sub CreateQueryTable()

Dim qtbSales As QueryTable

Dim sqlString As String

Dim connString As String

sqlString = "SELECT * FROM 2002Sales ORDER BY Goal DESC"

connString = _

"ODBC;DSN=MS Access Database;DBQ=H:\...\MthSales.mdb"

Set qtbSales = ActiveSheet.QueryTables.Add(Connection:=connString, _

Destination:=Range("a3"), Sql:=sqlString)

qtbSales.Name = "SalesQuery"

qtbSales.Refresh

End Sub

External Data Range Properties Dialog Box

Exhibit 8-8: The External Data Range Properties dialog box

SQL(Structured Query Language)

SQL, pronounced like the word “sequel,” stands for Structured Query Language

SQL is a set of commands, or statements, that allow you to access and manipulate the data stored in many database management systems

SQL is not case sensitive, but programmers use capital letters for SQL keywords

The SQL SELECT Statement

The most commonly used SQL command is the SELECT statement

The SELECT keyword allows you to select which database fields (and records) you want to view

Separate field's by comma, or use an asterisk (*) to select all fields

You can also control the order in which the fields and records appear

SELECT FirstName, LastName FROM tblStudent;

SELECT tblStudent.FirstName, tblStudent.LastName FROM tblStudent;

SELECT LastName FROM tblStudent WHERE City = ‘Des Plaines’;

SELECT LastName FROM tblStudent WHERE City = ‘Skokie’ OR City= ‘Niles’;

SELECT LastName FROM tblStudent WHERE City LIKE ‘D*’;

SELECT LastName FROM tblStudent ORDER BY FirstName , City DESC;

SQL SELECT Examples

Basic Syntax and Examples of the SQL SELECT Statement

Exhibit 8-10: The basic syntax and examples of the SQL statement

The SQL SELECT Statement

The ORDER BY field part of the syntax—referred to as the ORDER BY clause—allows you to control the order in which the records appear when displayed

After assigning a SELECT statement to the CommandText property, you then must use the QueryTable object’s Refresh method to update the query table

The Refresh method tells Microsoft Excel to connect to the query table’s data source, execute the query that appears in the CommandText property, and then return the appropriate data to the query table

Creating the DisplaySalesMacro Procedure

The DisplaySales macro should allow anyone to display, in the Sales worksheet, the sales for either all of the stores on only a specific store

It also should calculate the difference between the monthly sales goals and the actual sales made

Pseudocode for theDisplaySales Procedure

Exhibit 8-11: The pseudocode for the Display Sales procedure

Word Lesson:Viewing the Data Source and

the Main Document The mail merge feature in Word allows you

to merge a Word document, called the main document, with the data contained in adata source

The data source can be another Word document, an Access database, an Outlook contact list, an Excel worksheet, or some other source

Before creating the procedure, open Nancy’s main document, which is a Word document stored on your Data Disk

You will use this document to generate the Willowtown Health Club labels

The MailMerge Object

You use the MailMerge object’s Destination property to control the destination of the merged documents

The MailMerge Object

To select the records to be merged with the main document, you use the syntax mailMergeObject.DataSource.QueryString = query, where query is a string that represents a valid SQL SELECT statement

Exhibit 8-12: The valid settings for the MailMerge object’s destination property

The SQL SELECT Statement

Different applications handle the capitalization of SQL keywords in different ways

In this book, you will be entering all SQL keywords in uppercase letters

The full syntax of the SELECT statement contains other clauses and options that are beyond the scope of this book

To display records in descending order, add the keyword DESC after field in the ORDER BY clause

After selecting the appropriate records to merge, you use the MailMerge object’s Execute method to perform the mail merge

Pseudocode for the GenerateLabels Procedure

Exhibit 8-13: The pseudocode for the GenerateLabels procedure

Access Lesson:Creating the DisplayReport

Procedure Professor Martinez’s database is stored in the Student

Data folder on your hard disk

Begin by opening the database and viewing the Payments table

To open the Trip database and view the Payments table, double-click on Trip and Payments respectively

The database contains one table named Payments and one report named PayReport

The Payments table contains five fields: ID, LastName, FirstName, Paid, and Updated

Creating theDisplayReport Procedure

The Paid field, which stores the total amount paid by each student, is a Currency field

Pseudocode for the DisplayReport Procedure

Exhibit 8-14: The pseudocode for the DisplayReport procedure