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# Database Calculation

Posted on 2011-09-07
Medium Priority
244 Views
Last Modified: 2012-05-12
Hello,

I'm sure this will be a quick and easy one for you guys ...

I have a very simple database that stores the price of a commodity and the date that price was reported.  What I need to do is display the date and price (which I have already done), but I need to also display the difference between the current price and the previous price.  So, this week (9/7), it is 12.23, last week (8/31) it was 12.02, and the week before (8/24) it was 12.15.  I need to know how to display it like this:

9/7/11     \$12.23     +\$0.21     +1.75%
8/31/11   \$12.02      -\$0.13      -1.07%
8/24/11   \$12.15     +\$0.18     +2.11%

Where the difference and percentage is calculated based on the date and price.

I have the following code in the webpage to return the Price and Date:

``````	cmdSelect= New OleDbCommand( "SELECT * From OREO", objConn)
dtrReader= cmdSelect.ExecuteReader()
While dtrReader.Read()
Response.Write(dtrReader("CurrentPrice") & " - " & dtrReader("PriceDate") & "<br>")
End While
``````

I am using Access for the database.

Thanks!
0
Question by:PowerEdgeTech
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9 Comments

LVL 16

Expert Comment

ID: 36499196
Few options...

1.  Create an Access query with the calcs in it.  Then just run your Select statement against the query.
2.  Or calculate in the SQL Statement.
3.  Do calcs in .NET

then just format the output in .NET as a percent.
0

LVL 17

Expert Comment

ID: 36499218
It your change your select statement to sort in descending order you can calculate the differences easily. You need to store the previous value and compare to the next result. Something along the lines of
``````cmdSelect= New OleDbCommand( "SELECT * From OREO", objConn)
dtrReader= cmdSelect.ExecuteReader()
Dim tempVal as Double = 0.00

While dtrReader.Read()

Response.Write(dtrReader("CurrentPrice") & " - " & dtrReader("PriceDate")
If tempVal=0.00 Then
Response.Write("none<br />")
Else
Response.Write((tempVal-Convert.ToDouble(dtrReader("CurrentPrice"))).ToString() & "<br />")
End If

'set the new value
tempVal = Convert.ToDouble(dtrReader("CurrentPrice"))

End While
``````
0

LVL 17

Expert Comment

ID: 36499250
I'm sure there are simpler ways but if you wanted to sort with most recent at the top you could put the data in a datatable and manipulate through there. Below is something along the lines of what you might do to move the data into a datatable first then loop through each row to calculate, again there are easier ways to do this.
``````Dim dt As New DataTable()
dt.Columns.Add(New DataColumn("date"))
dt.Columns.Add(New DataColumn("amount"))
dt.Columns.Add(New DataColumn("diff"))
dt.Columns.Add(New DataColumn("diffp"))

Dim TempVal As Double = 0.0

While myReader.Read()
Dim newRow As DataRow = dt.NewRow()
newRow("date") = myReader("date")
newRow("amount") = myReader("amount")
dt.Rows.Add(newRow)
End While

For Each dr As DataRow In dt.Rows
If TempVal <> 0.0 Then
dr("diff") = (Convert.ToDouble(dr("diff")) - TempVal).ToString()
End If

TempVal = dr("amount")
Next
``````
0

LVL 18

Expert Comment

ID: 36499399
You can do it all in a query.

You need to get two adjacent rows into the same row, then perform the calculations.

SELECT T1.Date, T1.Product, T1.Price, T2.Price, T1.Price-T2.Price AS PriceChange,( (T1.Price / T2.Price)-1 ) * 100 AS ChangePercent
FROM Tt1 AS  T1  LEFT OUTER  JOIN Tt1 AS T2  ON  T2.Date < T1.Date  AND  T1.Product = T2.Product
WHERE T2.Date = (SELECT MAX(Date) FROM tt1 WHERE Product = T1.Product AND Date < T1.Date)

This works for a table with the design:
Date <DateTime>
Product <Text>
Price <Currency>
0

LVL 33

Author Comment

ID: 36499464
Thanks Ori ... it is giving me the differences now, but with 16 decimal places ... how can I chop the display down to 2 decimal places?  And to calculate the percentage using tempVal?  I've tried a few things, but none of them have worked.

Thanks.
0

LVL 17

Accepted Solution

OriNetworks earned 2000 total points
ID: 36524550

``````Dim dt As New DataTable()
dt.Columns.Add(New DataColumn("date"))
dt.Columns.Add(New DataColumn("amount"))
dt.Columns.Add(New DataColumn("diff"))
dt.Columns.Add(New DataColumn("diffp"))

Dim TempVal As Double = 0.0

While myReader.Read()
Dim newRow As DataRow = dt.NewRow()
newRow("date") = myReader("date")
newRow("amount") = myReader("amount")
dt.Rows.Add(newRow)
End While

For Each dr As DataRow In dt.Rows
If TempVal <> 0.0 Then
dr("diff") = Math.Round((Convert.ToDouble(dr("diff")) - TempVal).ToString(),2)
dr("diffp") = ((Convert.ToDouble(dr("diff")) / TempVal) * 100).ToString() & "%"
End If

TempVal = dr("amount")
Next
``````
0

LVL 33

Author Comment

ID: 36524660
Hi ... thanks Ori!

I get the following when running the page:

0

LVL 17

Expert Comment

ID: 36573229
change
dr("diff") = Math.Round((Convert.ToDouble(dr("diff")) - TempVal).ToString(),2)

to
dr("diff") = Math.Round(CDbl((Convert.ToDouble(dr("diff")) - TempVal).ToString()),2)
0

LVL 33

Author Closing Comment

ID: 36576520
Thanks.
0

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