1. 376a. Database Design Dept. of Computer Science Vassar College
Class 7: Domain Relational Calculus and beginning SQL
Prof. Billibon Yoshimi
11/7/2018

2. Housekeeping Reminder: Homework for Oct 2nd.
4.19, 7.20, 7.26, 9.11, 9.15, 9.20 (except h)
Midterm: October 9th (Wednesday)
Prof. Billibon Yoshimi
11/7/2018

3. So far… Should be able to draw ER and EER diagrams.
Need to work on constraints.
Relational data model.
How to convert ER and EER to Relational Model.
Understand tuples and tuple calculus
{e.name, e.address | EMPLOYEE(e) and (d) (DEPARTMENT(d) and d.DNAME=“research” and d.DNUMBER=e.DNO)
Prof. Billibon Yoshimi
11/7/2018

4. Safe expressions Expressions should return finite number of results.
{t | not (EMPLOYEE(t)) } is not safe.
Only considered safe if the results are from the domain of the range relation (right side).
Not (EMPLOYEE(t)) has tuples from outside the EMPLOYEE(t) relation.
Prof. Billibon Yoshimi
11/7/2018

5. One more calculus: Domain Relational Calculus
Domain relational calculus used in query by example.
Variables range of domains of attributes (instead of tuples.)
E.g.
{x1, x2..xn| COND(x1, x2..xn, ..xn+m}
xi range of domain of attribute Ai
Prof. Billibon Yoshimi
11/7/2018

6. Atoms are different Atom may be…
1. R(x1, x2, … xn) where r is a relation with degree n and each xi is a domain variable. In short hand R(x1 x2 … xn) no commas
2. xi. op xj. where op  { =, > , , <, , }. x’s are domain variables.
3. xi. op c where op  { =, > , , <, , } and xi is a domain variable.
*Normally use lowercase l-z for domain vars
Prof. Billibon Yoshimi
11/7/2018

7. Example Get birthdate and address of person named “John B. Smith”
{ uv | ( q) ( r) ( s) ( t) ( w) ( x) ( y) ( z) (EMPLOYEE (qrstwxyz) and q = ‘John’ and r=‘B.’ and s=‘Smith’)}
Every attribute of EMPLOYEE is assigned a domain var. only U and V are free.
Prof. Billibon Yoshimi
11/7/2018

8. Another way {q | EMPLOYEE( ‘John’,’B.’,’Smith’,t, u, v, w, x, y, z) }
All variables are free.
Prof. Billibon Yoshimi
11/7/2018

9. Example Name and address of everyone in research department
{qsv | ( z) ( l) ( m) (EMPLOYEE(qrstuvwxyz) and DEPT(lmno) and l=‘research’ and m=z)
EMPLOYEE(FNAME, MINIT, LNAME, SSN, BDATE, ADDRESS, SEX, SALARY, SUPERSSN, DNO)
DEPARTMENT(DNAME, DNUMBER, MGRSSN, MGRSTARTDATE)
Prof. Billibon Yoshimi
11/7/2018

10. Try a few
For every project in Stafford, list the controlling manager’s name and birthdate.
EMPLOYEE(FNAME, MINIT, LNAME, SSN, BDATE, ADDRESS, SEX, SALARY, SUPERSSN, DNO)
DEPARTMENT(DNAME, DNUMBER, MGRSSN, MGRSTARTDATE)
PROJECT(PNAME,PNUMBER, PLOCATION,DNUM)
rstv|EI Eo Ep Eu , PROJECT(jklm) and DEPARTMENT(nopq) and EMPLOYEE (rstuvwxyza) and l = ‘Stafford’ and m=o and p=u
Prof. Billibon Yoshimi
11/7/2018

11. Find employees with no dependents.
EMPLOYEE(FNAME, MINIT, LNAME, SSN, BDATE, ADDRESS, SEX, SALARY, SUPERSSN, DNO)
DEPARTMENT(DNAME, DNUMBER, MGRSSN, MGRSTARTDATE)
PROJECT(PNAME,PNUMBER, PLOCATION,DNUM)
WORKS_ON(ESSN,PNO,HOURS)
DEPT_LOCATIONS(DNUMBER,DLOCATION)
DEPENDENT(ESSN, DEPENDENT_NAME,SEX,BDATE,RELATIONSHIP)
Prof. Billibon Yoshimi
11/7/2018

12. List names of all managers with one dependent.
EMPLOYEE(FNAME, MINIT, LNAME, SSN, BDATE, ADDRESS, SEX, SALARY, SUPERSSN, DNO)
DEPARTMENT(DNAME, DNUMBER, MGRSSN, MGRSTARTDATE)
PROJECT(PNAME,PNUMBER, PLOCATION,DNUM)
WORKS_ON(ESSN,PNO,HOURS)
DEPT_LOCATIONS(DNUMBER,DLOCATION)
DEPENDENT(ESSN, DEPENDENT_NAME,SEX,BDATE,RELATIONSHIP)
Prof. Billibon Yoshimi
11/7/2018

13. SQL2 or SQL92 Related to relational algebra (types of operations)
Used by most commercial RDBMS.
Based on tuple calculus (declarative vs. procedural)
Used to define data and manipulate data.
Prof. Billibon Yoshimi
11/7/2018

14. Basic data types Table - relation Row - tuple Column - attribute
Schema - name, tables, constraints, views, domains and authorization.
Schemas allow multiple databases to exist on the same server.
Prof. Billibon Yoshimi
11/7/2018

15. CREATE SCHEMA Used to create new schema
E.g. CREATE SCHEMA MYCORPDB AUTHORIZATION YOSHIMI
Creates a new table to hold relations (tables) for the schema MYCORPDB. The owner of the database is YOSHIMI.
In MySQL use CREATE DATABASE no auth.
Prof. Billibon Yoshimi
11/7/2018

16. DROP SCHEMA When you’re done with the database.
In MySQL use DROP DATABASE <databasename>
Prof. Billibon Yoshimi
11/7/2018

17. CREATE TABLE Used to create a new relation. CREATE TABLE EMPLOYEE
( FNAME VARCHAR(15) NOT NULL,
MINIT CHAR,
LNAME VARCHAR(15) NOT NULL,
SSN CHAR(9) NOT NULL,
BDATE DATE,
ADDRESS VARCHAR(30),
SEX CHAR,
SALARY DECIMAL (10,2),
SUPERSSN CHAR(9)
DNO INT NOT NULL,
PRIMARY KEY (SSN),
FOREIGN KEY (SUPERSSN) REFERENCES EMPLOYEE(SSN),
FOREIGN KEY (DNO) REFERENCES DEPARTMEnT (DNUMBER));
Prof. Billibon Yoshimi
11/7/2018

18. CREATE TABLE Better way CREATE TABLE MYCORPDB.EMPLOYEE
(associate the table with the schema)
Prof. Billibon Yoshimi
11/7/2018

19. Basic data types INTEGER, INT or SMALLINT
FLOAT, REAL, DOUBLE PRECISION
DECIMAL( i, j) - total and fractional
CHAR, CHARACTER
VARCHAR
DATE - YEAR, MONTH, DAY
TIME - HOUR, MINUTE, SECOND
TIMESTAMP - DATE+TIME+6digit fract sec
(These are from p.387 of MySQL manual)
Prof. Billibon Yoshimi
11/7/2018

20. Constraints on variables
NOT NULL - must have a value
DEFAULT <value> - if no value is specified, use the following value.
Table constraints include
PRIMARY KEY (attribute list)
FOREIGN KEY (attribute) REFERENCES <foreign key>
UNIQUE - specifies alternate key
Label constraints using
CONSTRAINT ESSPK PRIMARY KEY (SSN)
Prof. Billibon Yoshimi
11/7/2018

21. Referential Integrity
Through FOREIGN KEY.
Referential triggered action (ON DELETE) (ON UPDATE):
- SET NULL
- CASCADE
- SET DEFAULT
Prof. Billibon Yoshimi
11/7/2018

22. Example
EMPLOYEE( …
SUPERSSN CHAR (9),
FOREIGN KEY(SUPERSSN) REFERENCES EMPLOYEE(SSN)
ON DELETE SET NULL
When supervisor is deleted, set this field to NULL.
Prof. Billibon Yoshimi
11/7/2018

23. Example
EMPLOYEE( … SUPERSSN CHAR (9), FOREIGN KEY(SUPERSSN) REFERENCES EMPLOYEE(SSN) ON UPDATE CASCADE
If SSN of manager is corrected, results propagate to manager’s workers.
Prof. Billibon Yoshimi
11/7/2018

24. Use CASCADE
For relationships like WORKS_ON, multi-valued attributes like DEPT_LOCATION and weak entities.
Prof. Billibon Yoshimi
11/7/2018

25. Remember… Rows are not ordered.
Attributes for a given relation have an implicit order.
Prof. Billibon Yoshimi
11/7/2018

26. DROP TABLE When you’re finished with a table.
VERY DANGEROUS. WILL destroy entire table.
Prof. Billibon Yoshimi
11/7/2018

27. ALTER TABLE Used to add/remove/modify attributes (domains).
Used to add/remove/modify constraints
ALTER TABLE MYCORPDB.EMPLOYEE ADD PAYSCALE CHAR(3);
Why can’t you have a NOT NULL constraint on a new attribute?
Prof. Billibon Yoshimi
11/7/2018

28. Other ALTER TABLE operations
ALTER TABLE EMPLOYEE DROP PAYSCALE CASCADE;
ALTER TABLE EMPLOYEE DROP PAYSCALE DEFAULT; cancel the default value
ALTER TABLE EMPLOYEE SET DEFAULT ‘001’
ALTER TABLE EMPLOYEE DROP CONSTRAINT EMPPK CASCADE;
Prof. Billibon Yoshimi
11/7/2018

29. SELECT statement No relation to sigma
SQL tables are not sets (they’re multi-sets).
Use DISTINCT to regain set-like quality.
Basically:
SELECT
<attribute list>
FROM
<list of tables>
WHERE
<condition list>
Prof. Billibon Yoshimi
11/7/2018

30. Get the birthdate and address of employees with the name “John B
Get the birthdate and address of employees with the name “John B. Smith”
R.A.
SELECT
BDATE, ADDRESS
FROM
EMPLOYEE
WHERE
FNAME=“JOHN” and MINIT=“B” and LNAME=“SMITH”
Prof. Billibon Yoshimi
11/7/2018

31. Can use SELECT to do join operation too
FNAME, ADDRESS
FROM
EMPLOYEE, DEPARTMENT
WHERE
DEPARTMENT=“RESEARCH” AND DNUMBER=DNO
Print the firstname and address of all employees in the research department.
Prof. Billibon Yoshimi
11/7/2018

32. Resolving ambiguous names
Relationships may have same named attributes.
Use relation.attribute to disambiguate.
When using multiple instances of a relation in a SELECT, use aliases..
SELECT
E.FNAME, E.LNAME, S.FNAME, S.LNAME
FROM
EMPLOYEE as E, EMPLOYEE as S
WHERE
E.SUPERSSN = S.SSN
Prof. Billibon Yoshimi
11/7/2018

33. Can also create attribute aliases,
EMPLOYEE AS E(FN,MI,LN,SSN,BD,ADDR,S,SAL,SSSN,DNO)
Prof. Billibon Yoshimi
11/7/2018

34. SELECT - FROM statements
Unspecified where is *.
If multiple relations are specified in FROM then CROSSPRODUCT
Prof. Billibon Yoshimi
11/7/2018

35. Other modifiers to SELECT
SELECT * FROM - WHERE
* - Selects all attributes
SELECT ALL x FROM WHERE
- get all values, including duplicates
SELECT DISTINCT * FROM WHERE
- removes duplicates *EXPENSIVE*
Prof. Billibon Yoshimi
11/7/2018

36. UNION, EXCEPT and INTERSECT operations
(SELECT *) UNION (SELECT *)
Sub sets should be union compatible, same attribute tuples, same ordering.
Prof. Billibon Yoshimi
11/7/2018

37. Comparing strings In WHERE statements use LIKE
WHERE NAME LIKE “%ITH%”
% - replaces arbitrary numbers of characters
_ - replaces a single character
“_____5_____”
In MySQL, use REGEX too.
^ - match beginning of line
$- match end of line
[bB] - match any one char in bracket
* - zero or one instances of preceding thing
Match anywhere in the input, unlike LIKE
Prof. Billibon Yoshimi
11/7/2018

38. Operations on return values
+,-,*,/
|| is string append,
Prof. Billibon Yoshimi
11/7/2018

39. SELECT FROM WHERE ORDER BY
ORDER BY attribute ASC|DESC, attribute ASC|DESC
By default it is in ascending order.
Order on first attribute, then second,then third.
Prof. Billibon Yoshimi
11/7/2018

40. More complex queries. Nexted queries
WHERE X IN takes (SELECT as argument)
Prof. Billibon Yoshimi
11/7/2018