Microsoft KB Archive/107748

= VB3 Creating a Parameter Query in Visual Basic for Windows =

Article ID: 107748

Article Last Modified on 1/8/2003

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APPLIES TO


 * Microsoft Visual Basic 3.0 Professional Edition

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This article was previously published under Q107748



SUMMARY
This article explains how to create and use a parameter query. A parameter query is a type of QueryDef specific to Visual Basic and Microsoft Access. Parameter queries enable you to automate the process of changing query criteria. With a parameter query, you can set new values for the parameters each time you run the query.



MORE INFORMATION
A parameter query is created in a program by using the CreateQueryDef function. Here is the syntax for the CreateQueryDef function:   Set querydef = database.CreateQueryDef(name, sqltext)

querydef - a QueryDef object database - a Database object name    - string containing query name sqltext - string containing the SQL query text The sqltext string is optional or it can be defined by using the .SQL property of the QueryDef. To create a parameter query, place the PARAMETERS statement in the sqltext string. Here is the syntax for the PARAMETERS statement:   PARAMETERS parametertext datatype

parametertext - name of the parameter datatype     - type of the parameter The following table lists the appropriate Microsoft Access SQL datatype that should be used with the PARAMETERS statement as well as the corresponding Microsoft Access field type, Visual Basic variable type, and constant value from the DATACONS.TXT file.   Microsoft      Microsoft        Visual Access SQL    Access Field     Basic Type     DATACONS.TXT Constant -  Bit            Yes/No           Integer        DB_BOOLEAN = 1 Byte          Byte             Integer        DB_BYTE = 2 Short         Integer          Integer        DB_INTEGER = 3 Long          Long Integer     Long           DB_LONG = 4 Currency      Currency         Double         DB_CURRENCY = 5 IEEESingle    Single           Single         DB_SINGLE = 6 IEEEDouble    Double           Double         DB_DOUBLE = 7 DateTime      Date/Time        Variant        DB_DATE = 8 Binary        Binary           String Text          Text             String         DB_TEXT = 10 LongBinary    OLE Object       String         DB_LONGBINARY = 11 LongText      Memo             String         DB_MEMO = 12 Following the PARAMETERS statement in the sqltext string, place the query. The query can refer to the parameter (parametertext) named in the PARAMETERS statement. Wherever the query refers to a parameter the current value will be substituted when the query is executed.

For example, if the query text is:

  PARAMETERS i SHORT; SELECT fld FROM tbl WHERE fld=i and the parameter i was set to 42 in the program. The parameter i would be substituted and the resulting query would be equivalent to:   SELECT fld FROM tbl WHERE fld=42

Multiple Parameters in a PARAMETERS statement
It is also possible to have multiple parameters in a PARAMETERS statement. To do this, use commas to separate the parameters as follows:   PARAMETERS parametertext datatype, parametertext datatype, ... Prior to executing the query, set the parameters using this syntax:   querydef!parametertext = value

querydef     - a QueryDef object parametertext - the name of the parameter in the PARAMETERS statement value        - the value the parameter will have In the previous example, you would use QD!i=42 before executing the query.

Once the parameters are set, you are ready to execute the query. There are three methods (Execute, CreateDynaset, and CreateSnapshot) supported by a QueryDef that will cause the query to be executed.

More information on parameter queries is available in the Visual Basic, version 3.0, "Professional Features Book 2."

Example Parameter Queries
The following example illustrates the use of a short parameter in a query. The example has two parts. The first part creates a new QueryDef for BIBLIO.MDB (the sample Microsoft Access database that ships with Visual Basic) and should be executed only once. The second part uses the QueryDef to create a snapshot, which is then displayed. To test the example, place each of the following code segments in a command button Click event procedure: 'Create QueryDef "by date" Dim Db As Database Dim Qd As QueryDef Set Db = OpenDatabase("C:\VB\BIBLIO.MDB") Set Qd = Db.CreateQueryDef("By date") 'Create the query "By date" QdText = "PARAMETERS dp Short; " QdText = QdText & "SELECT * from Titles WHERE [Year Published] = dp" Qd.SQL = QdText Print Qd.SQL Qd.Close Db.Close

' Create Snapshot from QueryDef Dim Db As Database Dim Qd As QueryDef Dim Sn As Snapshot Set Db = OpenDatabase("C:\VB\BIBLIO.MDB") Set Qd = Db.OpenQueryDef("By Date") 'Open the "By date" query Qd!dp = 1991                        'Set the value of the dp parameter Set Sn = Qd.CreateSnapshot        'Create a snapshot from the query Sn.MoveFirst Do Until Sn.EOF For i = 1 To Sn.Fields.Count - 1 Print Sn(i);                  'Display results of query Next Print Sn.MoveNext Loop Sn.Close Qd.Close Db.Close The second example shows how to use an action parameter query. Note that action queries are invoked with the Excute method, not CreateDynaset or CreateSnapshot, because they do not return records: 'Create QueryDef Dim Db As Database Dim Qd As QueryDef Set Db = OpenDatabase("C:\VB\BIBLIO.MDB") Set Qd = Db.CreateQueryDef("Delete by name") 'Create the query QdText = "PARAMETERS p1 Text; " QdText = QdText & "DELETE * FROM Authors WHERE Author = p1;" Qd.SQL = QdText Print Qd.SQL Qd.Close Db.Close

' Execute the QueryDef Dim Db As Database Dim Qd As QueryDef Set Db = OpenDatabase("C:\VB\BIBLIO.MDB") Set Qd = Db.OpenQueryDef("Delete by name") Qd!p1 = "Bob" Qd.Execute          'Perform the action query Qd.Close Db.Close

Additional query words: 3.00 parameterized querydefs

Keywords: KB107748

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