Microsoft KB Archive/105539
Article ID: 105539
Article Last Modified on 1/8/2003
- Microsoft Visual Basic 3.0 Professional Edition
This article was previously published under Q105539
You can have a Visual Basic application build a SQL query based on choices made by a person using the application. The application can then use the SQL query when creating a view into a database.
This article describes methods developers can use to create SQL queries that are based on control properties or names of variables. The information in this article applies to the following methods: FindFirst, FindLast, FindNext, FindPrevious, CreateDynaset, CreateSnapshot, Execute, and ExecuteSQL.
When building a SQL query, do not include the variable or control name inside the SQL string; instead, you should reference its value. Using the variable or control name inside the SQL string is a mistake. For example, the following code is incorrect:
Dim ds As Dynaset ds.FindFirst "NameField = Text1.Text" 'this code is incorrect
This code is trying to create a dynaset that finds the first occurrence of the contents of Text1 in a field called NameField. Although the code will not produce an error, it will not find the desired value. It will search for the first occurrence of the string "Text1.Text" not the value of the Text1.Text control property.
The criteria being sought is a string, so the programmer must use string concatenation rules to build the criteria string. The following gives the correct version of the code example:
Dim ds As Dynaset ds.FindFirst "NameField = '" & Text1.Text & "'"
The ampersand (&) operator concatenates the strings together correctly. Also, in SQL syntax, you need to enclose string data in single quotation marks to differentiate strings from variables.
If you think the corrected version looks confusing with all the single and double quotation marks, you can assign the criteria to a string. Then use Debug.Print to view the contents of the string. The following is the same example enhanced to take advantage of the debug window:
Dim ds As Dynaset Dim SQL$ as String SQL$ = "NameField = '" & Text1.Text & "'" Debug.Print SQL$ ds.FindFirst SQL$
If Text1 contains the string "Wilson," the Debug windows displays:
NameField = 'Wilson'
If the data type of a field is a number instead of a string, don't enclose the value being sought in single quotation marks. For example, use the following code to create a dynaset that finds the first occurrence of a zip code in a field called ZipCodeField where the ZipCodeField data type is not a string:
Dim ds As Dynaset Dim ZipCodeVar as Double Dim SQL$ as String ZipCodeVar = 98052 SQL$ = "ZipCodeField = " & ZipCodeVar 'This line builds the string Debug.Print SQL$ ds.FindFirst SQL$
Additional query words: 3.00 pitfall RecordSource