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POGrouping data slows query despite 25% decrease in the number of results
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9785529
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AnswerCount
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2012-03-20T11:04:27.743
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2012-03-22T08:52:11.513
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2012-03-20T11:32:24.767
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Body
I have an Access database of 4M rows, each representing an individual customer order. I need to run a query from Excel (I use VBA) in order to retrieve only the orders from customers in <code>REGION1</code>. I tried the following (names should be pretty self-explanatory): <pre><code>Sub Query() Dim cn As Object Dim strFile As String Dim strCon As String Dim strSQL As String strFile = "C:\Users\MyName\Desktop\DataBase.accdb" strCon = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" & strFile Set cn = CreateObject("ADODB.Connection") Set rs = CreateObject("ADODB.Recordset") cn.Open strCon strSQL = "SELECT [CUSTOMER], [DATE], [REVENUE]" _ & "FROM [SALES DB]" _ & "WHERE [REGION]='REGION1'" rs.Open strSQL, cn, 0, 1 Worksheets(1).Cells(2, 1).CopyFromRecordset rs rs.Close Set rs = Nothing cn.Close Set cn = Nothing End Sub </code></pre> This works nicely but it's a bit slow, as it returns ~600k rows. So I thought: "Who cares about the detailed list of all customer orders? I just need the monthly aggregate. This should reduce the number of returned rows and hence inprove speed!". So I changed my code to: <pre><code>strSQL = "SELECT [CUSTOMER], MONTH([DATE]), YEAR([DATE]), SUM([REVENUE])" _ & "FROM [SALES DB]" _ & "WHERE [REGION]='REGION1'" & "GROUP BY [CUSTOMER], MONTH([DATE]), YEAR([DATE])" </code></pre> As I expected, now only ~450K results show up. The thing is, the query actually became slower. I'm actually better off extracting the ungrouped data and then aggregating it with a simple pivot table. How can less data be slower to extract? I know there's some calculations to be performed in between, but still. Does anybody out there have any idea how I can overcome this problem?
Tags
<performance><ms-access><vba><group-by>
Title
Grouping data slows query despite 25% decrease in the number of results
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1. PO
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1. USBruder
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1. USBruder
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