ID: Q136062
The information in this article applies to:
Advanced: Requires expert coding, interoperability, and multiuser skills.
This article demonstrates how to use a form to specify the criteria for a query that is dynamically built by a Visual Basic for Applications function. This technique is called query by form (QBF).
This article assumes that you are familiar with Visual Basic for Applications and with creating Microsoft Access applications using the programming tools provided with Microsoft Access. For more information about Visual Basic for Applications, please refer to your version of the "Building Applications with Microsoft Access" manual.
NOTE: A demonstration of the technique used in this article can be seen in the sample file, Qrysmp97.exe. For information about how to obtain this sample file, please see the following article in the Microsoft Knowledge Base:
ARTICLE-ID: Q182568
TITLE : ACC97: Microsoft Access 97 Sample Queries Available on
MSL
You can use the QBF method to specify the criteria for filtering an existing query, but this method can become complex when you add more fields to the form. For example, one such complication arises when you do not enter a value in one of the form's criteria fields.
A more flexible QBF method is to use a Visual Basic function to dynamically create the SQL statement for a query that is deleted and recreated each time the function runs. This method avoids using an empty criteria field as part of the query's WHERE condition.
Concatenating (joining) SQL statements in Visual Basic requires that you "type cast" fields with special characters to instruct the Microsoft Jet database engine what field data types you are using. The following type- casting characters are used in this article:
Field Type Type-Casting Character
------------------------------------------
Text Single quotation mark (')
Date Number sign (#)
Numeric None
NOTE: In the following sample statements, an underscore (_) at the end of a line is used as a line-continuation character. Remove the underscore from the end of the line when re-creating these statements.
Text: "Select * from [Orders] where [ShipCity] = '" & [Mycriteria] _
& "' ;"
Date: "Select * from [Orders] where [OrderDate] = #"& [Mycriteria] _
& "# ;"
Numeric: "Select * from [Orders] where [EmployeeID] = "& [Mycriteria] _
& ";"
1. Open the sample database Northwind.mdb and create a new, blank form
based on the Orders table.
box as follows:
Text box 1:
Name: Customer ID
Text box 2:
Name: Ship City
Text box 3:
Name: Ship Country
Text box 4:
Name: Employee ID
Text box 5:
Name: Order Start Date
Text box 6:
Name: Order End Date
Name: cmdRunQuery
Caption: Run Query
procedure:
Private Sub cmdRunQuery_Click()
Dim db As Database
Dim QD As QueryDef
Dim where As Variant
Set db = CurrentDb()
' Delete the existing dynamic query; trap the error if the query does
' not exist.
On Error Resume Next
db.querydefs.Delete ("Dynamic_Query")
On Error GoTo 0
' Note the single quotation marks surrounding the text fields [Ship
' Country] and [CustomerID].
' Note that there are no type-casting characters surrounding the
' numeric field [EmployeeID].
where = Null
where = where & " AND [ShipCountry]= '" + Me![Ship Country] + "'"
where = where & " AND [CustomerID]= '" + Me![Customer Id] + "'"
where = where & " AND [EmployeeID]= " + Me![Employee Id]
'NOTE: In Microsoft Access 97, when you use the plus sign (+) in an
'expression in which you are concatenating a variable of the numeric
'data type, you must use parenthesis around the syntax, as in the
'following example:
'
' where = where & (" AND [EmployeeID]= " + Me![Employee Id])
'
'You must also use a conversion function to make sure that the proper
'conversion (to either NULL or String) takes place.
' The following section evaluates the ShipCity criteria you enter.
' If the first or last character of the criteria is the wildcard
' character (*), then the function uses the "LIKE" operator in the
' SQL statement instead of "=". Also note the single quotation
' marks surrounding the text field [ShipCity].
If Left(Me![Ship City],1) = "*" Or Right(Me![Ship City],1) = "*" Then
where = where & " AND [ShipCity] like '" + Me![Ship City] + "'"
Else
where = where & " AND [ShipCity] = '" + Me![Ship City] + "'"
End If
' Note the number signs (#) surrounding the date field [Order Date].
If Not IsNull(Me![Order End Date]) Then
where = where & " AND [OrderDate] between #" + _
Me![Order Start Date] + "# AND #" & Me![Order End Date] & "#"
Else
where = where & " AND [OrderDate] >= #" + Me![Order Start Date] _
+ " #"
End If
' Remove the following MsgBox line if you do not want to display the
' SQL statement.
' NOTE: The Mid function is used in the following MsgBox function to
' remove the word AND that follows the first Where clause. If you do
' not use the Mid function, the SQL statement contains the word AND
' at the beginning of the WHERE clause, for example:
'
' Select * from Orders where AND [CustomerID] = 'CACTU'
MsgBox "Select * from Orders " & (" where " + Mid(where, 6) & ";")
Set QD = db.CreateQueryDef("Dynamic_Query", _
"Select * from orders " & (" where " + Mid(where, 6) & ";"))
DoCmd.OpenQuery "Dynamic_Query"
End Sub
6. To run the query, enter the following sample criteria in the text boxes,
and then click the command button:
Customer ID text box: CACTU
Ship City text box: BU*
Employee ID text box: 8
Order Start Date text box: 1/1/94
For more information about the CreateQueryDef method, search for "CreateQueryDef method" using the Microsoft Access 97 Help Index.
For more information about SQL, search for "SQL statements, writing and Generating," and then "Build SQL Statements That Include Variables and Controls" using the Microsoft Access 97 Help Index.
For more information about the QBF technique, search for "query by form" using the Microsoft Access 97 Help Index. Or see the following articles here in the Microsoft Knowledge Base:
ARTICLE-ID: Q95931
TITLE : ACC: How to Use the Query-by-Form (QBF) Technique
ARTICLE-ID: Q109334
TITLE : ACC: How to Dynamically Create a Filter
ARTICLE-ID: Q117544
TITLE : ACC2: Query by Form (QBF) Using Dynamic QueryDef
Keywords : kbusage QryHowto
Version : 7.0 97
Platform : WINDOWS
Hardware : x86
Issue type : kbhowtoLast Reviewed: November 21, 1998