Some slide content courtesy of Susan Davidson & Raghu Ramakrishnan
Zachary G. Ives
University of Pennsylvania
CIS 550 – Database & Information Systems
September 18, 2003

 Please turn in your answers to HW1 now
 Please take a copy of HW2
 Sign up for Oracle account at: http://www.seas.upenn.edu/ora/
 (Those who don’t have eniac accounts: please email me)
 Remember, decisions about groups and projects due by end of Friday in email
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We’re Studying SQL: A Friendly Face
Over the Tuple Relational Calculus
SELECT [DISTINCT] {T
1
FROM {relation} T
1
.attrib, …, T
, {relation} T
WHERE {predicates}
2
, …
2
.attrib} from-list select-list qualification
 Queries can have set operators (UNION, EXCEPT,
…)
 Queries can be nested
 Often multiple ways of expressing the same query
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 GROUP BY
SELECT {group-attribs} , {aggregate-operator}(attrib)
FROM {relation} T
1
, {relation} T
2
, …
WHERE {predicates}
GROUP BY {group-list}
 Aggregate operators
 AVG , COUNT , SUM , MAX , MIN
 DISTINCT keyword for AVG , COUNT , SUM
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 Number of students in each course offering
 Number of different grades expected for each course offering
 Number of (distinct) students taking AI courses
5

STUDENT sid name
1 Jill
2 Qun
3 Nitin
4 Marty
Takes sid exp-grade
1 A
1
3
A
A
3
4
C
C cid
550-0103
700-1003
700-1003
501-0103
501-0103
COURSE cid
550-0103
700-1003
501-0103 subj sem
DB
AI
F03
S03
Arch F03
PROFESSOR Teaches
2
8 fid
1 name
Ives
Saul
Roth fid cid
1 550-0103
2 700-1003
8 501-0103
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What If You Want to Only Show
Some Groups?
 The HAVING clause lets you do a selection based on an aggregate (there must be 1 value per group):
SELECT C.subj, COUNT(S.sid)
FROM STUDENT S, Takes T, COURSE C
WHERE S.sid = T.sid AND T.cid = C.cid
GROUP BY subj
HAVING COUNT(S.sid) > 5
 Exercise: For each subject taught by at least two professors, list the minimum expected grade
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Aggregation and Table Expressions
(aka Derived Relations)
 Sometimes need to compute results over the results of a previous aggregation:
SELECT subj, AVG(size)
FROM (
SELECT C.cid AS id, C.subj AS subj,
COUNT(S.sid) AS size
FROM STUDENT S, Takes T, COURSE C
WHERE S.sid = T.sid AND T.cid = C.cid
GROUP BY cid, subj)
GROUP BY subj
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 Tables are great, but…
 Not everyone is uniform – I may have a cell phone but not a fax
 We may simply be missing certain information
 We may be unsure about values
 How do we handle these things?
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 We designate a special “null” value to represent
“unknown” or “N/A”
Name Home Fax
Sam 123-4567 NULL
Li 234-8972 234-8766
Maria 789-2312 789-2121
 But a question: what does:
SELECT * FROM CONTACT WHERE Fax < “789-1111” do?
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 Need ways to evaluate boolean expressions and have the result be “unknown” (or T/F)
 Need ways of composing these three-state expressions using AND , OR , NOT :
T AND U = U T OR U = T
F AND U = F F OR U = U NOT U = U
U AND U = U U OR U = U
 Can also test for null-ness: attr IS NULL , attr IS NOT
NULL
 Finally: need rules for arithmetic, aggregation
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 Sometimes need special variations of joins:
 I want to see all courses and their students
 … But what if there’s a course with no students?
 Outer join:
 Most common is left outer join:
SELECT C.subj, C.cid, T.sid
FROM COURSE C LEFT OUTER JOIN Takes T
ON C.cid = T.cid
WHERE …
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STUDENT sid name
1 Jill
2 Qun
3 Nitin
4 Marty
Takes sid exp-grade
1 A
1
3
A
A
3
4
C
C cid
550-0103
700-1003
700-1003
501-0103
501-0103
COURSE cid
550-0103
700-1003
501-0103
555-0103 subj sem
DB
AI
F03
S03
Arch F03
Food F03
PROFESSOR Teaches
2
8 fid
1 name
Ives
Saul
Roth fid cid
1 550-0103
2 700-1003
8 501-0103
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 Oracle doesn’t support standard SQL syntax here:
SELECT C.subj, C.cid, T.sid
FROM COURSE C , Takes T
WHERE C.cid =(+) T.cid
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 Can have much more complex ideas of incomplete or approximate information
 Probabilistic models (tuple 80% likely to be an answer)
 Naïve tables (can have variables instead of NULLs)
 Conditional tables (tuple IF some condition holds)
 … And what if you want “0 or more”?
 In relational databases, create a new table and foreign key
 But can have semistructured data (like XML)
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Modifying the Database:
Inserting Data
 Inserting a new literal tuple is easy, if wordy:
INSERT INTO FACULTY(fid, name)
VALUES (4, ‘Simpson’)
 But we can also insert the results of a query!
INSERT INTO FACULTY(fid, name)
SELECT sid AS fid, name
FROM STUDENT
WHERE sid < 20
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 Deletion is a fairly simple operation:
DELETE
FROM STUDENT S
WHERE S.sid < 25
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 What kinds of updates might you want to do?
UPDATE STUDENT S
SET S.sid = 1 + S.sid, S.name = ‘Janet’
WHERE S.name = ‘Jane’
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 Generally, apps are in a different (“host”) language with embedded SQL statements
 Static: SQLJ, embedded SQL in C
 Runtime: ODBC, JDBC, ADO, OLE DB, …
 Typically, predefined mappings between host language types and SQL types (e.g., VARCHAR  string or char[])
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EXEC SQL BEGIN DECLARE SECTION int sid; char name[20];
EXEC SQL END DECLARE SECTION
…
EXEC SQL INSERT INTO STUDENT
VALUES (:sid, :name);
EXEC SQL
SELECT name, age
INTO :sid, :name
FROM STUDENT
WHERE sid < 20
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The Impedance Mismatch and Cursors
 SQL is set-oriented – it returns relations
 There’s no relation type in most languages!
 Solution: cursor that’s opened, read
DECLARE sinfo CURSOR FOR
SELECT sid, name FROM STUDENT
…
OPEN sinfo; while (…) {
FETCH sinfo INTO :sid, :name
…
}
CLOSE sinfo;
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 Roughly speaking, a Java version of ODBC
 See Chapter 6 of the text for more info
} import java.sql.*;
Connection conn = DriverManager.getConnection(…);
PreparedStatement stmt = conn.prepareStatement(“SELECT * FROM STUDENT”);
…
ResultSet rs = stmt.executeQuery(); while (rs.next()) { sid = rs.getInteger(1);
…
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 We all know traditional static HTML web sites:
Web-Browser
HTTP-Request
GET ...
Web-Server
HTML-File
Load File
File-System
HTML-File
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Can have the web server invoke code (with parameters) to generate HTML
HTTP-Request
HTML-File
Web Server
Web Server
Load File
File-System
HTML
HTML?
Output Program?
Execute Program
File
I/O, Network, DB
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 Advantages:
 Standardized: works for every web-server, browser
 Flexible: Any language (C++, Perl, Java, …) can be used
 Disadvantages:
 Statelessness: query-by-query approach
 Inefficient: new process forked for every request
 Security: CGI programmer is responsible for security
 Updates: To update layout, one has to be a programmer
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Java Applet
TCP/UDP
IP
Java-Server-Process
JDBC Driver manager
JDBC-
Driver
JDBC-
Driver
JDBC-
Driver
Sybase Oracle ...
Browser
JVM
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 Advantages:
 Can take advantage of client processing
 Platform independent – assuming standard java
 Disadvantages:
 Requires JVM on client; self-contained
 Inefficient: loading can take a long time ...
 Resource intensive: Client needs to be state of the art
 Restrictive: can only connect to server where applet was loaded from (for security … can be configured)
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*SP Server pages
(IIS, Tomcat, …)
HTTP Request
HTML File
Web Server
Web Server
Load File
File-System
HTML
Output
HTML?
Script?
Server Extension
File
I/O, Network, DB
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One Step Beyond: DB-Driven Web
Sites (Strudel, Cocoon, …)
HTTP Request
HTML File
Web Server
DB-Driven Web Server
Cache
Styles
HTML
Dynamic
HTML
Generation
Script?
Data
Other data sources
Local
Database
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 We’ve seen how to query in SQL (DML)
 Basic foundation is TRC-based
 Subqueries and aggregation add extra power
 Nulls and outer joins add flexibility of representation
 We can update tables
 We’ve seen that SQL doesn’t precisely match standard host language semantics
 Embedded SQL
 Dynamic SQL
 Data-driven web sites
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 Groups and project choices due by email by end of day tomorrow – send to zives@cis , dinkar@gradient.cis
 Sign up for your Oracle account ASAP
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