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Introduction to Databases for Web Developers
Putting it all together with a DBI-Aware CGI Script  
I have prepared a little DBI script for us to walk through. You can copy this over to your system, change the setup variables and it should run on your system as well. The code of this should all be straight forward and you should have all read the Perl tutorials at Web Ware, so I won't spend much time documenting the code.

     # First we identify the location of
     # the Perl interpreter. You will need
     # to change this line to reflect the
     # location of Perl on your system.


     # Next we will tell Perl that we are
     # going to USE the DBI and CGI
     # modules.
     # We will use the CGI module mainly
     # to handle incoming form data.
     # The CGI::CARP module has a nice
     # feature called "fatalsToBrowser"
     # that sends error messages to the
     # web browser window so that the
     # user does not get a meaningless
     # 500 Server Error message.

use DBI;
use CGI;
use CGI::Carp qw(fatalsToBrowser);

     # Setup some implementation
     # specific variables. $dbname
     # is going to be the Data
     # Source name that you
     # assigned to your database in
     # the 32Bit ODBC Control
     # Panel plus the DBI:ODBC
     # pre-tag.  I did not setup
     # any security on my database
     # since it is only for local
     # testing, so we can leave
     # those values blank

$dbName     = "DBI:ODBC:MyCompany";
$dbUserName = "";
$dbPassword = "";

     # We will create a new CGI
     # object and use it to send
     # out the HTTP header and
     # to parse out the incoming
     # form variables "requestType"
     # and "sql".  You will see
     # where those form variables
     # come from in just a bit.

$dataIn       = new CGI;
$requestType  = $dataIn->param('requestType');
$sql  = $dataIn->param('sql');

     # Next we will check to see
     # if there is a value coming
     # in from a form for the
     # variable "sql".  If there
     # is no value, then we know
     # that the user has not yet
     # seen the submission form.
     # In that case, we will send
     # them the HTML form so they
     # can actually submit a value
     # for "sql". The following
     # screen shot shows you what
     # will be returned.
[SQL Entry Form]

if ($sql eq "")
    print qq!
             TEXT = "000000">
             ACTION = "dbi_demo.cgi">
    <TABLE BORDER = "1">
    <TH>Enter SQL
                        SIZE = "40"
                        NAME = "sql">
                        NAME = "requestType"
                        VALUE = "Submit SQL">

     # If there was a value for $sql, we know
     # that the user has already seen the
     # HTML form and has submitted some
     # SQL for us to process.  In that case,
     # we will open a connection to the
     # database, execute the SQL, gather
     # the result set and display it
     # to the user.  In the case of a
     # simple SELECT, we will display
     # the results in an HTML table.
     # If, on the other hand, the SQL
     # was a DELETE, MODIFY or INSERT,
     # we will let them know that the
     # operation was successful.
     # Notice that you need to do a lot
     # of dereferencing with the returned
     # rows :)
[SQL Entry Form]
    $dbh = DBI->connect($dbName,
    $dataObject = $dbh->prepare($sql);
    @dbRows = $dataObject->
    if ($sql =~ /^SELECT/i)
        print qq!
        <TITLE>SQL Statement
                 TEXT = "000000">
        <TABLE BORDER = "1">!;
        foreach $rowReference (@dbRows)
            foreach $columnReference
                print qq!<TR>!;
                foreach $column
                    print qq!<TD>
                print qq!</TR>!;
        print qq!
        print qq~Your SQL Query has been
               processed, please hit the
               back button and submit a
               SELECT to see the changes!~;

Well, however simple that application is, it should be enough to get you started. You will have to design your own application logic for a more useful databse tool, but all the components for a full featured application are demonstrated here.

As it so happens, I wrote a more complex application that you can use if you'd like. This application handles inserts, selects, updates and deletes in a much more user-friendly way. If you want to see the code, click here. Otherwise check out the screen shot of the interface.

[Demo Application]

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