creating databases for web applications

Creating Databases for Web Applications

3-Tier. Design vs Function vs Content. More SQL. More php.

Homework: work on final projects

Refrain on 3 tier

• Some divide the html tier into content versus style, with CSS holding the style. This is the interaction tier.– Note: Flash and other languages (Processing,

Java, ??) also do more function

• Middle tier, php, do 'business logic', other function.

• Information tier, MySQL, holds information! – Serves multiple functions. Implemented (possibly) by

different groups in an enterprise.

Another tier?

or is the 3 tier terminology insufficient

• Organizations use code and content developed and maintained by others.– Web services– cloud computing– content such as Google maps– ???

Extra credit opportunity to report / comment.

More SQL

Assuming the simple student database (id, sname, department, gpa)

• Produce a list of departments, with number of students, average, maximum, and minimum gpa

• Produce a list of departments, number of students with gpa at least 2 (not on academic probation?)

• Produce a list of departments, number of students on academic probation, limit to the 5 with the most on academic probation

Students in clubs

• Assume the student table (sid, sname, dept, gpa) plus 2 more tables – clubs: clubid, clubname, clubdesc– clubmemberships: mid, sid, clubid

• Usual technique, similar to tags, ordered items.

Generate list of students in club named Hiking

SELECT s.sname FROM students as s, clubs as c, clubmemberships as m WHERE c.clubname='Hiking' AND m.clubid=c.clubid AND s.sid=m.sid

ALTERNATIVE (may need parentheses) SELECT s.sname FROM students as s

JOIN clubmemberships as m ON m.sid = s.sid JOIN clubs as c WHERE clubname='Hiking' ON m.clubid=c.clubid

Extra credit

• (Difficult to check without creating all the tables, but try)

• Generate list of club names, count of students in clubs, ordered from most to least

Left Join

• Matches rows of two tables using the ON condition, but if something on the LEFT does not have a match, generate a row with null values.

• Used in the quiz show to find questions that haven't been answered or asked recently.

• NOTE: can have SELECT within a SELECT

Students not in any club

SELECT sname FROM SELECT * FROM students as s LEFT JOIN clubmemberships as m ON s.sid=m.sid WHERE m.sid=null

php to php

• One way to acquire and pass information from one php script to another is to use the query string.

• In the store application, html is produced that has <a> tags with href=makeorder.php?3

for example, where 3 represents a product id.

Select product: <table><?php$query="Select * from catalog";$result=mysql_db_query($DBname, $query, $link);while ($row=mysql_fetch_array($result)) { print ("<tr><td><a href=makeorder.php"); print ("?p_id="); print($row['id']); print(">"); print($row['p_name']); print("</a></td>"); print("<td><img src=\""); $picture=$row['picture']; print("$picture"); print("\" width='200'></td></tr>");}print ("</table>");

php to php

• Alternative to cookies or data passed via query strings are Sessions.

• The sessions may be passed via the HTTP headers– Extra credit opportunity: research and do posting on

php Sessions• Access and set using $_SESSION.• This, like $_COOKIE, etc. is an associative

array: accessed using names not indices.– NOTE: the shopping cart in my store application is

stored as a Session variable and is itself an associative array.

• <?php• session_start();• if (!isset($_SESSION["cart"])) {• $_SESSION['cart']=array();• $_SESSION['items'] = 0;• $_SESSION['totalprice']=0.00;• $cart = array();• }• else {• //print ("cart already started ");• $cart = $_SESSION['cart'];• }• ?>

<html><head><title>Shopping Cart</title><?require("displaycartfunction.php");?></head><body><?phprequire("opendbo.php");?><h1>Shopping cart</h1> <p><?if (isset($_GET['productid'])) { $p_id = $_GET['productid']; $quantity=$_GET['quantity']; $cart[$p_id] = $quantity; $_SESSION['cart'] = $cart; }

displaycart();

?>

<hr>

<a href="submitorder.php"> Checkout (submit order)! </a>

<a href="orderproduct.php"> More shopping! </a>

</body> </html>

displaycart

• Function stored in file displaycartfunction.• Assumes that connection has been made and

session started.• Makes use of the foreach construction for

associative arrays.– Since associative arrays don't use index values 0 to

length of array, what is the code to examine each element?

• Answer: foreach($aa as $key=>$qty) { }assuming $aa is the associative array and $key and $qty are variables used in the loop for the keys and values

– Makes use of number_format($totalprice,2) to produce dollars and cents

<?php//assumes that opendbo called, and session

started when call is made.function displaycart() { global $cart, $DBname, $link, $totalprice; print ("<table border=1>"); print ("<tr><td> Product ID </td> <td> Product

Name </td><td> Quantity </td> <td> Total cost </td> </tr>"); $items = 0; //note session variable items not used $totalprice = 0.00; $cart = $_SESSION['cart'];

foreach (@$cart as $pid => $qty) { $items += $qty; //print(" the pid is ".$pid . " and the qty is ". $qty); $query="Select * from catalog where id='$pid'"; //print("query is $query"); $result = mysql_db_query($DBname, $query, $link); $item_price = mysql_result($result,0,"cost"); $item_name = mysql_result($result,0,"p_name"); $item_total_price = $item_price * $qty; $totalprice += $item_total_price; $item_total_pricef = number_format($item_total_price,2); print ("<tr><td> $pid </td> <td> $item_name </td><td>

$qty </td> <td> $item_total_pricef </td> </td> ");

}

$totalpricef = "$" . number_format($totalprice,2);

print("<tr> <td> TOTALS </td> <td> </td> <td> $items items</td><td> $totalpricef </td></tr> </table>");

$_SESSION['items']=$items;

$_SESSION['totalprice']=$totalprice;

}

?>

Class work

• Gather around someone with laptop.

• Each group find different uses of JOIN (inner join) and LEFT JOIN to explain.

Homework

• Work on final projects.

creating databases for web applications

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