Displaying "Similar" or "Related" Vehicles - sql

Question

I have a vehicle database and would like to show "related" vehicles when a user clicks to view a vehicle. For instance, the user views a '2013 Chevy Tahoe' that is listed by dealership 'ABC Dealers'.
I need to create a SQL statement to grab 4 vehicles that are similar to the vehicle they are viewing. Here is the order of importance for now:
1) Dealer Listings (d_id)(Show vehicles also listed by that dealer)
2) Vehicle Category (vc_id)(Vehicle category such as Car, Truck, SUV, etc.)
3) Vehicle Make (vm_id)(Vehicle make such as Ford, Chevy, Lexus, etc.)
I have created a SQL statement, but it does not seem to do what I am looking for it to do. Can anyone offer any suggestions on how to properly build a SQL statement to grab the most relevant records in the order defined above?
strSQL = "SELECT TOP 4 v.v_id, vm.vm_name, v.v_year, v.v_model, v.v_search_price, d.d_name, u.u_name " & _
"FROM tbl_Vehicles v " & _
"LEFT JOIN tbl_VehicleMake vm ON vm.vm_id = v.vm_id " & _
"LEFT JOIN tbl_Dealers d ON d.d_id = v.d_id " & _
"LEFT JOIN tbl_Users u ON u.u_id = v.u_id " & _
"WHERE v.v_processed = 1 AND v.v_active = 1 AND v.v_id <> " & v_id
If Not CheckBlank(d_id) Then
strSQL = strSQL & " OR v.d_id = " & d_id
End If
If Not CheckBlank(vm_id) Then
strSQL = strSQL & " OR v.vm_id = " & vm_id
End If
If Not CheckBlank(vc_id) Then
strSQL = strSQL & " OR v.vc_id = " & vc_id
End If
strSQL = strSQL & " ORDER BY v.d_id, v.vc_id, v.vm_id"

Answer 1

I have a couple of thoughts for you.
Your current query has some ANDs and some ORs. You may need brackets to indicate your preferred order of operations, for example:
strSQL = "SELECT TOP 4 v.v_id, vm.vm_name, v.v_year, v.v_model, v.v_search_price, d.d_name, u.u_name " & _
"FROM tbl_Vehicles v " & _
"LEFT JOIN tbl_VehicleMake vm ON vm.vm_id = v.vm_id " & _
"LEFT JOIN tbl_Dealers d ON d.d_id = v.d_id " & _
"LEFT JOIN tbl_Users u ON u.u_id = v.u_id " & _
"WHERE v.v_processed = 1 AND v.v_active = 1 AND v.v_id <> " & v_id
If Not CheckBlank(d_id) Or Not CheckBlank(vm_id) Or Not CheckBlank(vc_id) Then
strSQL = strSQL & "("
End If
If Not CheckBlank(d_id) Then
strSQL = strSQL & " OR v.d_id = " & d_id
End If
If Not CheckBlank(vm_id) Then
strSQL = strSQL & " OR v.vm_id = " & vm_id
End If
If Not CheckBlank(vc_id) Then
strSQL = strSQL & " OR v.vc_id = " & vc_id
End If
If Not CheckBlank(d_id) Or Not CheckBlank(vm_id) Or Not CheckBlank(vc_id) Then
strSQL = strSQL & ")"
End If
strSQL = strSQL & " ORDER BY v.d_id, v.vc_id, v.vm_id"
But based on what you wrote in your question, you may be better with a query that uses the ORDER BY clause to get the most appropriate records based on the criteria you specified.
strSQL = "SELECT TOP 4 v.v_id, vm.vm_name, v.v_year, v.v_model, v.v_search_price, d.d_name, u.u_name " & _
"FROM tbl_Vehicles v " & _
"LEFT JOIN tbl_VehicleMake vm ON vm.vm_id = v.vm_id " & _
"LEFT JOIN tbl_Dealers d ON d.d_id = v.d_id " & _
"LEFT JOIN tbl_Users u ON u.u_id = v.u_id " & _
"WHERE v.v_processed = 1 AND v.v_active = 1 AND v.v_id <> " & v_id & " ORDER BY"
If Not CheckBlank(d_id) Or Not CheckBlank(vm_id) Or Not CheckBlank(vc_id) Then
If Not CheckBlank(d_id) Then
strSQL = strSQL & " CASE WHEN v.d_id = " & d_id & " THEN 0 ELSE 1 END,"
End If
If Not CheckBlank(vm_id) Then
strSQL = strSQL & " CASE WHEN v.vm_id = " & vm_id & " THEN 0 ELSE 1 END,"
End If
If Not CheckBlank(vc_id) Then
strSQL = strSQL & " CASE WHEN v.vc_id = " & vc_id & " THEN 0 ELSE 1 END,"
End If
strSQL = Left(strSQL, Len(strSQL) - 1)
Else
strSQL = strSQL & "v.d_id, v.vc_id, v.vm_id"
End If
This query will still give you results even if there are no vehicles for that dealer, make or category, so you will always have related vehicles (assuming you have at least 5 records).

Answer 2

It looks like the OR clauses you're using are not going to bring you you want. Assuming I'm understanding the snippet and the unseen db correctly, you need to create a subclause of the OR statements that is "ANDED" in. Try the following, after the initial strSQL assignment:
...
dim strSubClause
strSubClause = ""
If Not CheckBlank(d_id)) Then
strSubClause = "v.d_id = " & d_id
End If
If Not CheckBlank(vm_id) Then
If len(strSubClause) > 0 then
strSubClause = strSubClause & " OR v.vm_id = " & vm_id
Else
strSubClause = "v.vm_id = " & vm_id
End If
End If
If Not CheckBlank(vc_id) Then
If len(strSubClause) > 0 then
strSubClause = strSubClause & " OR v.vc_id = " & vc_id
Else
strSubClause = "v.vc_id = " & vc_id
End if
End If
If len(strSubClause) > 0 then
strSQL = " AND (" & strSubClause & ")"
End If
strSQL = strSQL & " ORDER BY v.d_id, v.vc_id, v.vm_id"
So, assuming all of your checks came back with values, you'd have a where clause that looks like:
...WHERE v.v_processed = 1 AND v.v_active = 1 AND v.v_id <> NNN AND (v.d_id = XXX OR v.vm_id = YYY OR v.vc_id = ZZZ) ORDER BY v.d_id, v.vc_id, v.vm_id
Does that make sense and/or get you closer or all the way to where you're wanting to go?