Web program-SQL.pptx Web program-SQL.pptx

Aug 6, 2024 Advanced Programming
Spring 2002
Henning Schulzrinne
Dept. of Computer Science
Columbia University

Aug 6, 2024 2
Advanced Programming
Spring 2002
SQL basics
 relational database: tables with labeled
columns, combined into database
 columns are atomic types:
create table person (
person integer unsigned auto_increment
primary key,
name varchar(40),
state enum ('', 'AK', 'AL', ...),
biography text,
verified date,
index(name)
)

Aug 6, 2024 3
Spring 2002
SQL basics
 Integer: tinyint, smallint,
mediumint, int(eger), bigint
 Floating point: float, double, real
 Decimal: decimal(m,d) (for $)
 Date: date, datetime, timestamp,
time, year
 String: char(N), varchar(N),
tinyblob, tinytext, blob, text,
enum, set

Aug 6, 2024 4
Spring 2002
SQL basics
 Retrieval: SELECT field1, field2
FROM table WHERE condition ORDER
BY expression
 Insertion: INSERT table SET
field1=value1,field2=value2, ...
 Update: UPDATE table SET
field1=value1, field2=value2
WHERE expression
 Delete row: DELETE FROM table WHERE
expression

Aug 6, 2024 5
Spring 2002
SQL basics: joins
 Join two tables that have a common
value ("product")
 e.g., SELECT lastname,city.name FROM
person,city WHERE city.zip=person.zip AND
lastname='Jones'

Aug 6, 2024 7
Spring 2002
SQL Python interface
import MySQLdb
import MySQLdb.cursors
try:
db = connect(host='grandcentral',
user='cs3995', passwd='cs3995',
db='grades')
except MySQLdb.Error, e:
print "Error %d: %s" % (e.args[0], e.args[1])
sys.exit(1)
c = db.cursor()
c.execute("SELECT ... FROM ...")
results = c.fetchall() # list of tuples
c.close()

Aug 6, 2024 8
Spring 2002
SQL Python interface
 Results are just tuples, with fields in
order of table definition
 can also fetch one row at a time:
c.execute("SELECT firstname,lastname FROM
students ORDER BY lastname")
print "<ul>"
while (1):
student = c.fetchone()
if student == None: break
print "<li>", student, student[0]
print "</ul>"

Aug 6, 2024 9
Spring 2002
Python SQL – dictionary
cursor
 Map rows to dictionary elements instead of
list elements:
c.close()
c = db.cursor(MySQLdb.cursors.DictCursor)
c.execute("SELECT firstname,lastname FROM
students")
results = c.fetchall()
for row in results:
print "%s, %s" % (row["firstname"],
row["lastname"])
print "%d rows were returned" % c.rowcount

Aug 6, 2024 10
Spring 2002
Servlet life cycle
 server application loads ServletClass
 creates instance via no-args
constructor
 servers call servlet's init() method
 server calls service(req, res)
method for each request (often, with
class name as URL), possibly
concurrently
 servers calls destroy() on shutdown

Aug 6, 2024 11
Spring 2002
HTTP requests as servlets
 HTTP method GET, PUT, POST, ... 
doGet, doPut, doPost
 subclass of HttpServlet overrides
default implementation

Aug 6, 2024 12
Spring 2002
Servlet example
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloClientServlet extends HttpServlet
{
protected void doGet(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException
{
res.setContentType("text/html");
PrintWriter out = res.getWriter();
out.println("<HTML><HEAD><TITLE>Hello Client!</TITLE>" +
"<HEAD><BODY>Hello Client!</BODY><HTML>");
out.close();
}
public String getServletInfo() {
return "HelloClientServlet 1.0 by Stefan Zeiger";
}
}

Aug 6, 2024 13
Spring 2002
2-tier architecture
 "client-server", "fat client"
 e.g., ODBC on client (PC), accessing
SQL database
 business logic on PC
 (-) transport data across network
 (-) need applications for each
platform
 (-) need to update applications on
many desktops

Aug 6, 2024 14
Spring 2002
n-tier architecture

Aug 6, 2024 15
Spring 2002
n-tier architecture
 client tier:
 receives user events (keyboard, mouse)
 presentation of data
 user interface
 e.g., Java applets, web browser, thin client
application
 application-server tier:
 "business logic"  actual data processing,
algorithms
 can be component-based (Java Beans)

Aug 6, 2024 16
Spring 2002
n-tier architecture
 Data-server tier
 data storage
 relational and legacy databases
 all tiers could run on same machine, but
usually separated
 HTTP (or SOAP) from client to server
 Corba or SOAP or remote-SQL between server
tiers
 Advantages:
 independent of storage model
 simpler authentication to database

Web program-SQL.pptx Web program-SQL.pptx

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