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Access Query Tips

Use indexes on the fields in the criteria section when using the query design screen. In other words, index the fields on the right hand side of a where clause.

Use an initial query screen as input to a second query. This limits the number of records required to respond to a new query request. Try splitting a complex query into two or more queries in order to give the user a rapid response.

Use a make table query when it isn't possible to split up a complex query. This approach won't speed up the initial query but can be useful when similar queries are done repeatedly. A 'make table' query saves intermediate results in a new table for future use, improving the efficiency of later queries.

Use stored queries only. A form that has a select statement as the record source either will not be optimized at all or will be optimized every time it runs.

Use recordset operations with the BeginTrans and CommitTrans methods in order to speed up query processing. This approach defines a transaction state which should include a relatively small number of statements.

Use recordset operations especially for an update or append query in order to increase the speed of your query from minutes to a few seconds. This approach has the greatest effect on complex rather than simple select queries since recordset operations are written to memory in a temporary transaction buffer rather than directly to the hard disk.

The following is a snippet of some code we use to analyze our website hits. The key parts of the Transaction processing are bolded.

Dim wksp As DAO.Workspace
Dim special As String
Dim visitor As String
Dim visit_date As Date
Dim Engine As String
Dim rst As DAO.Recordset
Dim rst2 As DAO.Recordset
Dim db As DAO.Database

Set db = CurrentDb
special = Chr(34) & "-" & Chr(34)
‘making Microsoft access databases run faster with better design
Set wksp = DBEngine.Workspaces(0) ' set up a transaction buffer
wksp.BeginTrans ' all record set changes are buffered after this
OnError GoTo roll0

Set rst2 = db.OpenRecordset("M_Sitestats")
Set rst = db.OpenRecordset("select field1 from Sitestats")
Do While Not rst.EOF
visitor = Left(rst!Field1, InStr(rst!Field1, " ") - 1)
visit_date = CDate(Mid(rst!Field1, InStr(rst!Field1, "[") + 1, 11))
If InStr(rst!Field1, "") <> 0 Then
Engine = "Google"
GoTo write_it
End If
If InStr(rst!Field1, "") <> 0 Then
Engine = "Yahoo"
GoTo write_it
End If

With rst2
!visitor = visitor
!visit_date = visit_date
!Engine = Engine
End With

wksp.CommitTrans ' here we write the changes to disk all at once

GoTo finish_it
If Err.Number = 3022 Then

On Error GoTo roll0
Resume check_next
End If
MsgBox Err.Number & " " & Err.Description
wksp.Rollback ' cancel everything if unexpected error


Set rst = Nothing
Set rst2 = Nothing

End Sub

This method can speed up queries by allowing the transactions to be cached rather than written to disk after each transaction.

If you haven't time to implement these tips or if the development resources available to you are unable to make progress, please contact us

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By Admin at 15 Mar 2016, 17:59 PM



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