Close method:
Closes an open DAO object (DAO object:An object that is defined by the Data Access Objects (DAO) library. You 
can use DAO objects, such as the Database, TableDef, Recordset, and QueryDef objects, to represent objects 
that are used to organize and manipulate data, such as tables and queries, in code.)

The object placeholder is an object variable that represents an open Connection, Database, Recordset, or 
Workspace object.

Remarks

Closing an open object removes it from the collection to which it's appended. Any attempt to close the default 
workspace is ignored.

Sub AddQuery()
Dim dbsNorthwind As DAO.Database
Dim qdfSalesReps As DAO.QueryDef
Dim rstSalesReps As DAO.Recordset
On Error GoTo ErrorHandler
   Set dbsNorthwind = CurrentDb
   Set qdfSalesReps = dbsNorthwind.CreateQueryDef( "SalesRepQuery" )
   qdfSalesReps.SQL =  "SELECT * FROM Employees WHERE Title = "  & _
                       "'Sales Representative'" 
   Set rstSalesReps = qdfSalesReps.OpenRecordset()
   'Call the function to add a constraint.
   AddQueryFilter rstSalesReps
   'Return database to original.
   dbsNorthwind.QueryDefs.Delete  "SalesRepQuery" 

   rstSalesReps.Close
   qdfSalesReps.Close '!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
   dbsNorthwind.Close
   Set rstSalesReps = Nothing
   Set qdfSalesReps = Nothing
   Set dbsNorthwind = Nothing
   Exit Sub
ErrorHandler:
   MsgBox  "Error #: "  & Err.Number & vbCrLf & vbCrLf & Err.Description
End Sub

You have not explicitly closed all DAO recordsets or query definitions in your Microsoft Access database. If 
you are using Visual Basic for Applications code to manipulate recordsets, QueryDefs, or recordset clones (on 
forms), in some cases you must explicitly close the object; otherwise, Microsoft Access does not close.

   Sub CloseObjects()
      Dim db As Database
      Dim rs As Recordset
      Dim qd As QueryDef
      Set db = CurrentDb
      Set rs = db.OpenRecordset( "Employees" , dbOpenTable)
      Set qd = db.QueryDefs( "Invoices" )
      rs.MoveLast
      MsgBox  "The Employees recordset is open."  & vbcr & _
          "The last Employee ID is "  & rs![EmployeeID] &  "." 
      Msgbox  "The Invoices query definition is open."  & vbcr & _
          "The first field in the query is "  & qd.Fields( 0 ).Name
      ' Explicitly close the Recordset and QueryDef objects.
      rs.Close
      qd.Close
   End Sub

   'Create QueryDef "by date"
   Dim Db As Database
   Dim Qd As QueryDef
   Set Db = OpenDatabase("C:\VB\BIBLIO.MDB")                 ' Old
   Set Db = DBEngine( 0 ).OpenDatabase( "C:\VB4-32 \BIBLIO.MDB") ' New
   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

Call this member function when you finish using the querydef object.

Closing the querydef releases the underlying DAO object but does not destroy the saved DAO querydef object or 
the C++ CDaoQueryDef object. This is not the same as CDaoDatabase::DeleteQueryDef, which deletes the querydef 
from the database's QueryDefs collection in DAO (if not a temporary querydef).

Function ParamQD()

    Dim dbSample As Database
    Dim qdfMyQuery As QueryDef
    Dim rstCountOrders As Recordset
    Dim strSearchName As String

    Set dbSample = CurrentDb()

    Set qdfMyQuery = dbSample.QueryDefs( "qryCustomerOrdersParameter" )
    
    ' Test for a value in the textbox
    If Not IsNull(Forms![frmSearch]![txtCustomerToFind]) Then
    
        ' Set the value of the parameter.
        strSearchName = Forms![frmSearch]![txtCustomerToFind]
        qdfMyQuery![Forms!frmSearch!txtCustomerToFind] = strSearchName

        ' Create the recordset (or dynaset).
        Set rstCountOrders = qdfMyQuery.OpenRecordset()
        If rstCountOrders.RecordCount =  0  Then
            MsgBox  "No records for "  & strSearchName
        Else
            rstCountOrders.MoveLast
            MsgBox rstCountOrders.RecordCount
        End If
        rstCountOrders.Close
    Else
        MsgBox  "Please enter a CustomerId in the textbox" 
    End If
    
    qdfMyQuery.Close
    dbSample.Close
    
End Function

One of the advantages of using prepared queries is that the query is compiled only once by the Microsoft Jet 
database engine. Further executions are very fast since Jet has already generated an execution plan for the 
query. However, the OLE DB provider for Jet doesn't take advantage of this optimization. Instead, it submits 
the prepared query to be re-compiled each time you re-query. When you use OLE DB, this requery is achieved in 
the following three steps:

 1 .Call IRowset::Close() to close the rowset returned by ICommand::Execute().
 2 .Change the parameter data.
 3 . Call ICommand::Execute() to create a new rowset based on the new parameters provided in step  2 .

   ' Modify the Query.
   Set DB = CurrentDb()
   Set Q = DB.QueryDefs( "MultiSelect Criteria Example" )
   Q.SQL =  "Select * From Orders Where [CustomerID] In("  & Criteria & _
      ");" 
   Q.Close