1. Creating Databases More SQL. Design. Original Project Assignment
Homework: Post proposal. Continue with planning.

2. MySQL
or most DBMS products can specify fields in records as FOREIGN KEY and do the work of checking.
My examples do not use this but instead do the checking in the php.

3. LOCK and UNLOCK
Most database applications are for use by multiple users. You don't want two or more users updating the same record
WHY NOT?
Most DBMS products have ways to support lengthy transactions.
POSTING OPPORTUNITY

4. Performance considerations
The CREATE table statement can specify one or more fields to be INDEX. This forces the DBMS to build an index (!) for improved speed. Trade off: more space and slightly more time when records added but shorter times during SELECT operations.
OPTIMIZE table. Assumption that tables become less efficient over time. Similar to disk defrag
EXPLAIN SELECT gives information on how this SELECT works. May lead you to revising the statement OR defining an INDEX (use ALTER table)
Other techniques….
Some DBMSs have stored procedures…

5. Recall
songs, features, featuresinsongs

6. Multiple tables conditions
SELECT from multiple tables (use commas)
List the name of the song with the name of the tag feature. One row for each tagging…
SELECT s.sname as a, f.fname as b FROM songs as s, featuresinsongs as t, features as f WHERE s.sid=t.sid AND t.fid=f.fid

7. Alternate Use INNER JOIN and ON
Note: the , between tables is equivalent to INNER JOIN
BUT
The way the operation is done is different and probably more efficient: this way doesn't create as many records. The WHERE way creates records for each row in one table with ALL rows of other table and then removes the ones not matching the WHERE conditions!

8. INNER JOIN ON
SELECT s.sname as a, f.fname as b FROM songs as s INNER JOIN featuresinsongs as t ON s.sid=t.sid INNER JOIN features as f ON t.fid=f.fid
NOTE: can say simply JOIN and not INNER JOIN
SELECT s.sname as a, f.fname as b FROM songs as s JOIN featuresinsongs as t ON s.sid=t.sid JOIN features as f ON t.fid=f.fid

9. Results in all cases This land is your land Folk
This land is your land Political
I told you so Political
something Pop
something else Classical

10. 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

11. 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.
Pop Quiz: Produce the ERD for this database

12. 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

13. 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

14. 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

15. php to php
One way to acquire and pass information from one php script to another is to use the query string.
In the origami store application, html is produced that has <a> tags with href=makeorder.php?3
for example, where 3 represents a product id.

16. 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>");

17. General principles for SQL
You need to build the Select statement
pencil in hand, work in steps
Decide the tables needed
Decide on logical conditions for records contributing to the result
WHERE
Decide on conditions connecting tables
JOIN ON 17

18. General principles, cont.
The GROUP BY command combines / aggregates records based on common values, using aggregate operations such as COUNT, AVG, SUM,etc.
If you want to maintain individual records but bunch them together, use ORDER
Remember order high to low requires DESC 18

19. General principles, cont.
For condition on which individual records to use: WHERE
For condition on aggregated (GROUP BY) records: HAVING
DISTINCT will extract [just] one from a table for the specified field 19

20. Operational definition
… is what you call the definition of something that is used in a process.
For example:
freshmen, sophomores, juniors, seniors
Dean's list, academic probation
??? 20

21. Unintended consequences
There was a rule that Dean’s List could only be awarded to students taking at least 12 credits.
12 credits was defined as 12 grade bearing credits
BUT what about seniors who earn SP (satisfactory progress) the first semester for 4 credit Senior Proejct
SP is the good grade. There is UP
After the second semester, the SP changes to final grade.

22. Aside Each Spring, we have a meeting for juniors aka rising seniors
I/we gave up on sending invitation to just that group and invited everyone.
We used .
We believe some rising seniors did not attend! 22

23. Generate a list of names of clubs
Just need one table
SELECT clubname FROM clubs
But what if I wanted clubs with members?
need the clubs table and the clubmemberships table
Join on cid 23

24. List of names of clubs with actual members
SELECT DISTINCT clubname FROM clubs as c JOIN clubmemberships as m ON c.cid=m.cid
could write c.clubname, but not needed since there is no ambiguity. Don't worry about this. 24

25. List names of clubs with at least 5 members
SELECT c.cid, c.clubname, COUNT(*) as n FROM clubs as c JOIN clubmemberships as m ON c.cid=m.cid GROUP BY c.cid HAVING n>=5
This produces more information than requested.
Could probably leave out the c.cid and instead GROUP by clubname. This would be better if there is a chance of ambiguity. 25

26. List names of any club with at least one freshmen
SELECT DISTINCT clubname FROM clubs as c JOIN clubmemberships as m ON c.cid=m.cid JOIN students as s ON m.sid=s.sid WHERE s.credits <30
Creating a table using the clubmembership table with information added from other tables.
Records only go into the table if the student's record has credits<30.
Use DISTINCT to get the distinct club names. Don't need other information. 26

27. List all clubs by name with number of sophomores
Need to use all 3 tables
Need to use WHERE clause to get sophomores
Operational definition: sophomore means between 30 and 60 credits.
Use LEFT JOIN to pick up clubs with no matches since for this example, I want clubs with no sophomores to show up!
Use COUNT(m.id) to NOT count any NULL fields! 27

28. [should check use of ( ) ]
SELECT clubname, COUNT(m.mid) as num from CLUBS as c LEFT JOIN (clubmemberships as m JOIN students as s ON m.sid = s.sid WHERE s.credits BETWEEN 30 AND 60) ON c.cid=m.cid
GROUP BY clubname 28

29. Possible result
Young Dems 40
Young Repubs 3
Origami 10
Hiking 0

30. Generate list of students with the clubs each one belongs to…
Curley
Circus
Hiking
PTV
Larry
Origami
Moe 30

31. Planning Will need SQL and then php
Need 3 tables (need club names and student names)
Need to place all records for each student together, but not aggregated. Use ORDER BY 31

32. SQL
SELECT s.sid, s.sname as a,c.clubname as b FROM students as s JOIN clubmemberships as m ON s.sid=m.sid JOIN clubs as c ON m.cid=c.cid ORDER BY s.sid s.sname
Note: information just in the clubmembership table isn't part of the resultset BUT those records are the only ones represented in the resultset. 32

33. php … // assume $result is the result of query $curstudent="";
print("<table border='1'><tr><th>Student</th><th>Club</th></tr>");
while ($row=mysql_fetch_array($result)) {
print("<tr><td>");
if ($curstudent!=$row['a']) {
$curstudent=$row['a'];
print("$curstudent</td>"); }
else {
print (" </td>"); }
print("<td>".$row['b']."</td></tr>");
print("</table>"); 33

34. Misc. Can order using multiple fields
….. ORDER BY lname, fname
WHERE or HAVING condition can use IN
…. WHERE clubname IN ('Hiking', 'Origami')
BETWEEN
… WHERE gpa BETWEEN 3 AND 4
ALSO can use BETWEEN for dates and times
NOTE: other ways to do these.
Extra credit opportunity: look up & report on ROLLUP 34

35. Planning
Planning (system design where design has broad meaning, not specifically the look)
comes first!
can change
Document the structure of database using ER diagram and the potential tasks (processes) of the application using the DFD
ER: entities and relationships
recall DFD: agents, processes, data stores 35

36. Database table design
Don't have same information in more than one table.
For example:
The records in an orders table points to a customer table. A customer's address is not in each order.

37. Data flow diagram place to specify
Processes: actions/tasks/operations of your application.
Agents: Who is doing what with/to information.
Data stores
This is an attempt to not be specific about how data kept.
Don't get bogged down in details of the information right now.

38. Presentation What is the application?
Show the information structure using an ER diagram.
Show the processes/operations/tasks using a Data flow diagram.
No storyboard (not yet)
May show a sketch of one or more screens.
Time for constructive comments from audience

39. Team work …. is not always smooth.
That is part of the reason for the assignments.
Do post names of everyone on the team.
Everyone should understand everything!
People do have different talents but EVERYONE can participate!

40. Comment
Large[r] organizations have elaborate tools for project proposals.
proposals
communication
testing
documentation
deployment.
Most work is incremental: fixing bugs and making enhancements.

41. Classwork/homework/classwork
Start/continue:
ideas, teams, planning
Next class: work session on planning
Following class: 4/24: Present plans using diagrams