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4GuysFromRolla.com : ASP FAQS : Databases, Queries

Question: How can I take the result of a SELECT...MULTIPLE or a group of same-named checkboxes and turn it into a query? That is, if the user selects 3 answers, how can I construct a query that looks for all 3?

Answer: To illustrate the request, let's assume that the form you will use looks like this:

<FORM Method="POST" ...>

Select one or more makes:
<SELECT Name="CarMake" MULTIPLE>
<OPTION>Chevrolet
<OPTION>Ford
<OPTION>Honda
<OPTION>Isuzu
<OPTION>Jeep
<OPTION>Lexus
<OPTION>Plymouth
<OPTION>Volkwagen
</SELECT>
<P>
Check the years you want to see reports for:
<INPUT Type=CheckBox Name="ReportYear" Value="1997"> 1997
<INPUT Type=CheckBox Name="ReportYear" Value="1998"> 1998
<INPUT Type=CheckBox Name="ReportYear" Value="1999"> 1999
<INPUT Type=CheckBox Name="ReportYear" Value="2000"> 2000
<INPUT Type=CheckBox Name="ReportYear" Value="2001"> 2001
<P>
<INPUT Type=Submit Value="Show reports...">
</FORM>


See that? In our next page, when we do

<%
makes = Request("CarMake")
years = Request("ReportYear")
%>

we will get multiple makes and/or years if the user selected more than one (makes) or checked more that one box (years).

But what is the form in which we get those multiple values?

Why not find out for yourself:

<%
Response.Write "Makes requested are: " & Request("CarMake") & "<P>"
Response.Write "Years requested are: " & Request("ReportYear") & "<P>"
%>


Did you do that? No? Well, I won't keep you in suspense. You would have seen something like

Ford, Honda, Plymouth
1997, 2000

depending, of course, on what the actual selections were.

Do you understand the format? You get a STRING that contains the individual items, separated from each other by COMMA-SPACE (a comma followed by a space...and please don't ask me why the silly space...some MS hotshot decided that one years ago!).

Now, the first thing that most people think of when they see a delimited string in VBScript is the SPLIT function. Nope. Not this time!

It turns out that SQL has a wonderful built-in ability to do exactly what we need! It is the WHERE fieldname IN ( item, item, item ) clause of SQL. And if you are not familiar with it, see the bottom of this page.

Actually, the list of ReportYears is already in the form we need for that clause! We could do this:

<%
years = Request("ReportYear") ' gets list: 1997,2000 etc.
...
SQL = "SELECT make, reportYear, rating, comments " _
        & "FROM carReportsTable " _
        & "WHERE reportYear IN (" & years & ")"
Set RS = yourConnection.Execute( SQL )
...
%>

Simple as that! We are done!

But that only works for numeric fields! For text and date fields, you need to surround each item in the list with the appropriate delimiters, such as WHERE ... IN ( 'item','item','item' ).

But good old Replace makes this easy!

<%
makes = Request("CarMake") ' gets list: Ford,Honda, ... etc.
makes = Replace( makes, ", ", "','" ) ' see below!
...
SQL = "SELECT make, reportYear, rating, comments " _
        & "FROM carReportsTable " _
        & "WHERE make IN ('" & makes & "')"
Set RS = yourConnection.Execute( SQL )
...
%>

See how that works? The Replace changes each COMMA-SPACE into APOSTROPHE-COMMA-APOSTROPHE!! And then we simply put an apostrophe on the front and back of the whole thing, and we have the proper form of list needed for the WHERE...IN... clause!

So the final form, combining both of those form fields is:

<%
years = Request("ReportYear") ' gets list: 1997,2000 etc.
makes = Request("CarMake") ' gets list: Ford,Honda, ... etc.
makes = Replace( makes, ", ", "','" ) ' see below!
...
SQL = "SELECT make, reportYear, rating, comments " _
        & "FROM carReportsTable " _
        & "WHERE make IN ('" & makes & "') "
        & "AND reportYear IN (" & years & ")"
Set RS = yourConnection.Execute( SQL )
...
%>





Further Information: If you are not familiar with the WHERE fieldname IN ( item, item, item ) clause of SQL, check out these pages:

One good place to start: Good intro! It says it is for SQL Server, but everything in it applies to all databases using ANSI-compliant SQL.

And this article goes into more detail, but ignores text and date fields. Doesn't use REPLACE as is done above. Note: there is a follow on article to this one that talks about "batch updates," but the title is misleading. He really shows "updates in a loop." The first article, above, shows a true example of a "batch delete."

And don't forget this really handy one-html-page summary of SQL.



FAQ posted by Bill Wilkinson at 4/19/2001 3:15:35 PM to the Databases, Queries category. This FAQ has been viewed 128,350 times.


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