Published: Friday, October 29, 1999
Returning a Random Number of Database Records
By Larry Boggs
While working on a web based competency-testing application I needed a way to return not just ONE random record but a group of random records. I searched the net high and low for a couple of months
trying to find something that would allow me do this. I eventually hunkered down and came up with my own way of doing this.
First comes the SQL statement to return the set of records you will pick your Random records from:
<%
strConnection="driver={Microsoft Access Driver (*.mdb)};dbq=" & server.mappath("/testdb.mdb")
strSQL = "SELECT id FROM tblQuestions"
set objConn = Server.CreateObject("ADODB.Connection")
Set objRst = Server.CreateObject("ADODB.Recordset")
objConn.Open strConnection
set objRst.ActiveConnection = objConn
objRst.LockType = adLockOptimistic
objRst.CursorType = adOpenKeySet
objRst.Open strSQL
%> |
Next, set the upper limit of the Randomize function by setting the variable rndMax equal to the RecordCount.
<%
objRst.MoveLast
cnt = objRst.RecordCount
cnt1 = cnt
rndMax = cnt
%> |
Next, set the number of records returned to either the number of questions they asked for or equal to the RecordCount.
<%
If CInt(Request.Form("maxNumber")) < cnt Then
cnt1 = CInt(Request.Form("maxNumber"))
End If
%> |
Now we want to return a Random number. Check if the variable str1 already contains that number. If so then that number is skipped
and it loops again returning another Random record number. This ensures that no values are repeated. If not then plug that number into
the str1 variable so we will know that that number has already been used the next time through the loop. If the random number is not
contained within the str1 variable then the value of the ID field is returned and plugged into the str1 variable. This loops until the
appropriate number of values have been plugged into the str1 variable.
<%
str = ","
str1 = ","
Do Until cnt1 = 0
Randomize
RndNumber = Int(Rnd * rndMax)
If (InStr(1, str1, "," & RndNumber & "," ) = 0) Then
str1 = str1 & RndNumber & ","
cnt1 = cnt1 - 1
objRst.MoveFirst
objRst.Move RndNumber
str = str & objRst("id") & ","
End If
Loop
%> |
Now we have a variable, (str), that contains a comma-delimited list of values from the ID field. Now, just reference the comma-
delimited string contained within the str1 variable in your SQL statement:
<%
sql = "SELECT * FROM tblQuestions WHERE (((InStr(1,'" & str & "',(',' & [id] & ',')))<>0)) "
%> |
This will return your Random set of records!
Try out the demo!
Here's the whole thing:
<!--Generate a random recordset from an Access database-->
<!--#include virtual="/adovbs.inc"-->
<%
Dim objConn
Dim objRst
Dim strSQL
Dim strConnection
Dim str
Dim str1
Dim cnt
Dim cnt1
Dim rndMax
Dim RndNumber
strConnection="driver={Microsoft Access Driver (*.mdb)};dbq=" & server.mappath("/testdb.mdb")
strSQL = "SELECT id FROM tblQuestions"
set objConn = Server.CreateObject("ADODB.Connection")
Set objRst = Server.CreateObject("ADODB.Recordset")
objConn.Open strConnection
set objRst.ActiveConnection = objConn
objRst.LockType = adLockOptimistic
objRst.CursorType = adOpenKeySet
objRst.Open strSQL
objRst.MoveLast
cnt = objRst.RecordCount
cnt1 = cnt
rndMax = cnt
If CInt(Request.Form("maxNumber")) < cnt Then
cnt1 = CInt(Request.Form("maxNumber"))
End If
str = ","
str1 = ","
Do Until cnt1 = 0
Randomize
RndNumber = Int(Rnd * rndMax)
If (InStr(1, str1, "," & RndNumber & "," ) = 0) Then
str1 = str1 & RndNumber & ","
cnt1 = cnt1 - 1
objRst.MoveFirst
objRst.Move RndNumber
str = str & objRst("id") & ","
End If
Loop
objRst.Close
Set objRst = Nothing
sql = "SELECT * FROM tblQuestions WHERE (((InStr(1,'" & str & "',(',' & [id] & ',')))<>0)) "
Set objRst = Server.CreateObject("ADODB.Recordset")
set objRst.ActiveConnection = objConn
objRst.LockType = adLockOptimistic
objRst.CursorType = adOpenKeySet
objRst.Open sql
%>
...DISPLAY THE RECORDS RETURNED...
<%
objRst.Close
Set objRst = Nothing
objConn.Close
Set objConn = Nothing
%>
|
I'd be interested in hearing from anyone that builds upon this and/or how they put it to use!
See Ya!
Larry Boggs
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