M.P. Johnson, DBMS, Stern/NYU, Spring C : Database Management Systems Lecture #16 M.P. Johnson Stern School of Business, NYU Spring, 2008

M.P. Johnson, DBMS, Stern/NYU, Spring Homework Project part 2 due Wed in class/by midnight Project part 3 posted soon…  Topic: populating your tables with data Later: Project part 5  Front-end

M.P. Johnson, DBMS, Stern/NYU, Spring Agenda: Programming for SQL Have now been exposed to:  Embedded SQL: Pro*C  Java JDBC All used; good to know about Most important for this course:  DB-conn from web scripting languages  PHP

M.P. Johnson, DBMS, Stern/NYU, Spring Goals: by next week Today: be able to post a hello-web PHP script in your i5 account Next week: Be able to write simple dynamic webpages in In PHP that 1. Take input from user 2. Execute SQL query 3. Display formatted results  Based on examples from class…

M.P. Johnson, DBMS, Stern/NYU, Spring New topic: web apps Goal: web front-end to database  Present dynamic content, on demand  Not canned (static) pages/not canned queries  (perhaps) modify DB on demand Naïve soln: static webpage & HTTP  index.html written, stored, put on server, displayed when it’s url is requested  HTTP is stateless (so?)  This doesn’t solve our problem

M.P. Johnson, DBMS, Stern/NYU, Spring Dynamic webpages Soln 1: upon url request 1. somehow decide to dynamically generate an html page (from scratch) 2. send back new html page to user  No html file exists on server, just created on demand  CGI/Perl, Java servlets, etc.

M.P. Johnson, DBMS, Stern/NYU, Spring New topic: CGI First, and still very popular method CGI: Common Gateway Interface  Not a programming language!  Just an interface (connection) between the webserver and an outside program “Webserver” = webserver software, e.g., Apache  Very simple basic idea: 1. user chooses an url 2.  webserver runs that url’s program, 3. sends back the program’s output

M.P. Johnson, DBMS, Stern/NYU, Spring On-the-fly content with CGI Program Client Server HTTP Request Data for program Generated HTML HTML Image from

M.P. Johnson, DBMS, Stern/NYU, Spring Using CGI CGI works with any prog./scripting lang. Really? Well, if things are set up right…

M.P. Johnson, DBMS, Stern/NYU, Spring CGI works… if the webserver machine can run program  pages/soho, not sales and if the user the webserver is running as (e.g. nobody) can can run your program and if the necessary jars/libraries are available and if nobody has permission to use them and if the necessary DB software is installed Plausible choices: Perl, Python, C, sh

M.P. Johnson, DBMS, Stern/NYU, Spring CGI admin Most webservers: CGI program/script must either 1. End in.cgi and/or 2. Reside in cgi-bin If an actual program, the cgi file is just the name of the executable: In a script, first (“shebang”) line says which interpreter to use: gcc -o myprog.cgi myproc.gcc #!/usr/local/bin/perl

M.P. Johnson, DBMS, Stern/NYU, Spring CGI input CGI programs must respond to input, two ways GET: string is part of the URL, following a ?: POST: string can be read by program from an environmental variable  Vars not visible to the browser user  Not automatically put in server log, etc.

M.P. Johnson, DBMS, Stern/NYU, Spring CGI summary One big advantage of CGI: not a language Existing command-line programs can be called from the web Web user can enter info Program output sent back as webpage Don’t want to start a new process for every user/pageview/roundtrip of your site?

M.P. Johnson, DBMS, Stern/NYU, Spring PHP-like scripting Program Client Server HTTP Request Data for program Generated HTML HTML Image from

M.P. Johnson, DBMS, Stern/NYU, Spring Dynamic webpages Original prob: need webpages to respond to user inputs Soln 2:  create a an html file embedded with special non- html code  upon url request, execute embedded code to generate more html/fill in the file  Send back the modified html page to user  An incomplete html page exists on server  Examples: PHP, JSPs, ASPs, etc.

M.P. Johnson, DBMS, Stern/NYU, Spring Review: dynamic webpages First option: for each request: run program, produce whole page, send back  CGI & some host language, Java Servlets, etc. Second option: create html page with missing parts; for each response, fill in the wholes and send back  Embedded scripting  PHP and others  PHP = Personal Home Page or = PHP Hypertext Processor – recursion

M.P. Johnson, DBMS, Stern/NYU, Spring Getting started Must set permissions in account on i5 Unix commands: ls, cd, pwn, cp, mv chmod command  Owner/group/all  Read/write/execute  Bitstrings…

M.P. Johnson, DBMS, Stern/NYU, Spring hello.php Q: What the difference between and \n? Hello from PHP Here comes the PHP part: \n"; ?> That's it! Hello from PHP Here comes the PHP part: \n"; ?> That's it!

M.P. Johnson, DBMS, Stern/NYU, Spring Script errors Script errors, w/ and w/o display_errors on:  Local dir must contain.htaccess:  Automatically load GET/POST params as vars   cp /home1/m/mpj3/public_html/php/.htaccess. php_flag display_errors on php_flag register_globals on php_flag display_errors on php_flag register_globals on

M.P. Johnson, DBMS, Stern/NYU, Spring PHP vars Names always start with $  <? $num1 = 58; $num2 = 67; print "First number ". $num1. " "; print "Second number ". $num2. " "; $total = $num1 + $num2; print "The sum is ". $total. " "; ?> <? $num1 = 58; $num2 = 67; print "First number ". $num1. " "; print "Second number ". $num2. " "; $total = $num1 + $num2; print "The sum is ". $total. " "; ?>

M.P. Johnson, DBMS, Stern/NYU, Spring Combining PHP and HTML <?php for($z=0;$z<=5;$z++) { ?> Iteration number <? } ?> <?php for($z=0;$z<=5;$z++) { ?> Iteration number <? } ?>

M.P. Johnson, DBMS, Stern/NYU, Spring More PHP syntax Somewhat C-like, somewhat Perl-like Case-sensitive Strings:  Concatenation op:.  Single, double quotes similar to Perl Comments:  # Unix shell-style  /* */ C-style  // C++-style Output:  echo(“hi there”);  print(“hi there”);  C’s printf

M.P. Johnson, DBMS, Stern/NYU, Spring PHP info PHP does not have both string and number ops like Perl Number ops treat (number) strings as numbers, regular strings as strings  Info function displays lots of server info: 

M.P. Johnson, DBMS, Stern/NYU, Spring New topic: HTML forms Interactive parts of HTML: forms Intuition for name: paper form  Fill in textboxes, check boxes or not, etc.  Turn it in (press button) HTML form  contains arb. # of INPUTs  Submits to somewhere (ACTION)  By GET or POST

M.P. Johnson, DBMS, Stern/NYU, Spring Form example On clicking Send, we go to the same page, but with “name=99&sumbit=OK” Enter a number: Enter a number:

M.P. Johnson, DBMS, Stern/NYU, Spring PHP and forms Obtain param a param, just prefix with $ (for now..) Goal: display text and button;  On submit, tell user what was entered Improve: also print, say, triple the input… if (isset($val)) print "You entered $val! "; if (isset($val)) print "You entered $val! ";

M.P. Johnson, DBMS, Stern/NYU, Spring PHP error-handling Many PHP scripts have lines of the form  some-statement OR die(“something happened”); What this means:  die exits with error message  PHP uses OR as and AND for bool operators  PHP supports boolean “short-circuiting” Boolean eval stops as fast as possible  Ftns often return 0/null/false for errors  if some-statement fails then we die

M.P. Johnson, DBMS, Stern/NYU, Spring New topic: PHP and databases PHP 5 has a JDBC-style DB interface But we’re using PHP 4.3.4… Special-purpose methods/libraries for MySQL, etc. Use these to obtain a connection, prepare and execute queries, etc.

M.P. Johnson, DBMS, Stern/NYU, Spring PHP & MySQL 1. Open a connection and open our DB: 2. Run query: $db = mysql_connect("mysql2.stern.nyu.edu:3306", user, pass); mysql_select_db("test", $db); $db = mysql_connect("mysql2.stern.nyu.edu:3306", user, pass); mysql_select_db("test", $db); $result = mysql_query($query,$db);

M.P. Johnson, DBMS, Stern/NYU, Spring PHP & MySQL 3. Extract next row of data from the results:  What this means: myrow is an array that can then be accessed  Other options, see code In general, to scroll through results, do: $myrow = mysql_fetch_row($result) while ($myrow = mysql_fetch_row($result)) # print row’s data while ($myrow = mysql_fetch_row($result)) # print row’s data

M.P. Johnson, DBMS, Stern/NYU, Spring Limit: PHP webpages that do something Semi-interesting PHP scripts:   Non-trivial but not huge: ~40 lines Works with two-column (a,b) table  Takes input from user  Returns rows whose a field contains value  If no/empty input, returns all rows Bad idea in general!

M.P. Johnson, DBMS, Stern/NYU, Spring lookup.php Two possible situations for running script: 1. Page opened for the first time 2. User entered parameter and pressed button Structure of file: 1. Print input box and button for next search  On button click, parameter is sent to this page’s url 2. (Try to) read input parameter 3. Open MySQL connection 4. Run query 5. Print results in a table 6. Disconnect from MySQL

M.P. Johnson, DBMS, Stern/NYU, Spring Higher-level structure As one page:  If we have params, display data based on them  Otherwise, prompt user for params, call self Could be:  Page 1: prompt for params, call page 2  Page 2: display data based on params In e.g.: always display data for convenience

M.P. Johnson, DBMS, Stern/NYU, Spring Insert/delete PHP example Similar to search example NB: form has two buttons

M.P. Johnson, DBMS, Stern/NYU, Spring Master-detail Perl/PHP example Idea: display list of regions;  When region clicked on, display its countries Mechanism: pass GET param in link, not with a FORM

M.P. Johnson, DBMS, Stern/NYU, Spring That’s all, folks! Q: Is this enough to get a job coding PHP? A: Probably not! But: a couple modified copies of lookup.php and/or cia.php + some HTML glue  fairly interesting site a couple modified copies of lookup.php and/or cia.php + some HTML glue  fairly interesting site

M.P. Johnson, DBMS, Stern/NYU, Spring For next time (in lab)… 1. Run/read these PHP scripts:       Go through at least one tutorial on PHP (on web/below) 3.Try posting a hello-web PHP script in your sales account Various others in dbms/php…dbms/php

M.P. Johnson, DBMS, Stern/NYU, Spring Tutorials on PHP Some material drawn from the following good tutorials: PHP introduction and examples:  Interactive PHP with database access:  Longer PHP/MySQL Tutorial from webmonkey:  Nice insert/update/delete example from webmonkey:  MySQL/Perl/PHP page from U-Wash: 