1. Structured Query Language (2) The main reference of this presentation is the textbook and PPT from : Elmasri & Navathe, Fundamental of Database Systems, 4 th edition, 2004, Chapter 8 Additional resources: presentation prepared by Prof Steven A. Demurjian, Sr (http://www.engr.uconn.edu/~steve/courses.html)

2. Slide 5-2 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 Outline Tables as Sets in SQL Substring pattern matching Arithmatic operation NULL values in SQL Nested queries EXISTS FUNCTION EXPLICIT SET & RENAMING ATTRIBUTE JOIN AGGREGATE FUNCTION GROUPING & HAVING CLAUSE

3. Slide 5-3 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 SET OPERATIONS SQL has directly incorporated some set operations There is a union operation (UNION), and in some versions of SQL there are set difference (MINUS) and intersection (INTERSECT) operations The resulting relations of these set operations are sets of tuples; duplicate tuples are eliminated from the result The set operations apply only to union compatible relations ; the two relations must have the same attributes and the attributes must appear in the same order

4. Slide 5-4 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 SET OPERATIONS (cont.) Query 4: Make a list of all project numbers for projects that involve an employee whose last name is 'Smith' as a worker or as a manager of the department that controls the project. Q4:(SELECT PNUMBER FROMPROJECT, DEPARTMENT, EMPLOYEE WHEREDNUM=DNUMBER AND MGRSSN=SSN ANDLNAME='Smith') UNION (SELECT PNUMBER FROMPROJECT, WORKS_ON, EMPLOYEE WHEREPNUMBER=PNO AND ESSN=SSN AND LNAME='Smith')

5. Slide 5-5 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 SUBSTRING COMPARISON The LIKE comparison operator is used to compare partial strings Two reserved characters are used: '%' (or '*' in some implementations) replaces an arbitrary number of characters, and '_' replaces a single arbitrary character

6. Slide 5-6 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 SUBSTRING COMPARISON (cont.) Query 12: Retrieve all employees whose address is in Houston, Texas. Here, the value of the ADDRESS attribute must contain the substring 'Houston,TX'. Q12:SELECT FNAME, LNAME FROM EMPLOYEE WHERE ADDRESS LIKE '%Houston, TX%’

7. Slide 5-7 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 SUBSTRING COMPARISON (cont.) Query 12A: Retrieve all employees who were born during the 1950s. Here, '5' must be the 8th character of the string (according to our format for date), so the BDATE value is '_______5_', with each underscore as a place holder for a single arbitrary character. Q12A:SELECT FNAME, LNAME FROMEMPLOYEE WHEREBDATE LIKE'_______5_’ If underscore or % is needed as a literal character in the string, the character should be preceded by an escape character (‘\’). ‘AB\_CD\%EF’ is represent ‘AB_CD%EF’

8. Slide 5-8 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 ARITHMETIC OPERATIONS The standard arithmetic operators '+', '-'. '*', and '/' (for addition, subtraction, multiplication, and division, respectively) can be applied to numeric values in an SQL query result Query 13: Show the effect of giving all employees who work on the 'ProductX' project a 10% raise. Q13:SELECT FNAME, LNAME, 1.1*SALARY AS INCREASED_SAL FROMEMPLOYEE, WORKS_ON, PROJECT WHERESSN=ESSN AND PNO=PNUMBER AND PNAME='ProductX’

9. Slide 5-9 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 ARITHMETIC OPERATIONS (2) Query 14: Retrieve all employees in department 5 whose salary is between $30,000 and $40,000 Q14:SELECT * FROMEMPLOYEE WHERE(SALARY BETWEEN 30000 AND 40000) AND DNO=5; Q14A:SELECT * FROMEMPLOYEE WHERE(SALARY >= 30000 AND SALARY <=40000) AND DNO=5;

10. Slide 5-10 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 ORDER BY The ORDER BY clause is used to sort the tuples in a query result based on the values of some attribute(s) Query 15: Retrieve a list of employees and the projects each works in, ordered by the employee's department, and within each department ordered alphabetically by employee last name. Q15: SELECT DNAME, LNAME, FNAME, PNAME FROM DEPARTMENT, EMPLOYEE, WORKS_ON, PROJECT WHEREDNUMBER=DNO AND SSN=ESSN AND PNO=PNUMBER ORDER BYDNAME, LNAME

11. Slide 5-11 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 ORDER BY (cont.) The default order is in ascending order of values We can specify the keyword DESC if we want a descending order; the keyword ASC can be used to explicitly specify ascending order, even though it is the default

12. Slide 5-12 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 NULLS IN SQL QUERIES SQL allows queries that check if a value is NULL (missing or undefined or not applicable) SQL uses IS or IS NOT to compare NULLs because it considers each NULL value distinct from other NULL values, so equality comparison is not appropriate. Query 18: Retrieve the names of all employees who do not have supervisors. Q18:SELECT FNAME, LNAME FROMEMPLOYEE WHERESUPERSSN IS NULL Note: If a join condition is specified, tuples with NULL values for the join attributes are not included in the result

13. Slide 5-13 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 NESTING OF QUERIES Some queries require that existing values in the database be fetched and then used in a comparison condition  using nested query A nested query is a complete SELECT-FROM-WHERE block within in the WHERE-clause of another query That other query is called the outer query Query 1A: Retrieve the name and address of all employees who work for the 'Research' department. Q1A:SELECT FNAME, LNAME, ADDRESS FROM EMPLOYEE WHERE DNO IN (SELECT DNUMBER FROM DEPARTMENT WHERE DNAME='Research' ) Outer Query Nested Query

14. Slide 5-14 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 NESTING OF QUERIES (cont.) The nested query selects the number of the 'Research' department The outer query select an EMPLOYEE tuple if its DNO value is in the result of either nested query The comparison operator IN compares a value v with a set (or multi-set) of values V, and evaluates to TRUE if v is one of the elements in V In general, we can have several levels of nested queries

15. Slide 5-15 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 NESTING OF QUERIES (cont.) SQL allows the use of tuples of values in comparisons by placing them within parentheses Query: retrieve the SSN from all employees who work the same (project,hours) combination on same project that employee ‘Jhon Smith’ (ESSN = ‘123456789’ works on. SELECT DISTINCT ESSN FROM WORKS_ON WHERE (PNO, HOURS) IN (SELECT PNO, HOURS FROM WORKS_ON WHERE ESSN = ‘123456789’);

16. Slide 5-16 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 NESTING OF QUERIES (cont.) Comparison operator can be used in nested query: >, >=, Keyword ALL can be used (v > ALL V)  returns TRUE if the value v is greater than all the values in the set (or multiset) V. Query: Return the names of employees whose salary is greater than salary of all the employees in department 5. SELECT LNAME, FNAME FROM EMPLOYEE WHERE SALARY > ALL (SELECT SALARY FROM EMPLOYEE WHERE DNO=5)

17. Slide 5-17 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 CORRELATED NESTED QUERIES If a condition in the WHERE-clause of a nested query references an attribute of a relation declared in the outer query, the two queries are said to be correlated The result of a correlated nested query is different for each tuple (or combination of tuples) of the relation(s) the outer query Query 16: Retrieve the name of each employee who has a dependent with the same first name and same sex as the employee. Q16: SELECT E.FNAME, E.LNAME FROMEMPLOYEE AS E WHERESSN IN (SELECTESSN FROMDEPENDENT WHERE FNAME=DEPENDENT_NAME AND E.SEX = SEX) Refer to sex attribute in outer query (EMPLOYEE)

18. Slide 5-18 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 CORRELATED NESTED QUERIES (cont.) A query written with nested SELECT... FROM... WHERE... blocks and using the = or IN comparison operators can always be expressed as a single block query. For example, Q12 may be written as in Q12A Q12A:SELECT E.FNAME, E.LNAME FROMEMPLOYEE E, DEPENDENT D WHEREE.SSN=D.ESSN AND E.FNAME=D.DEPENDENT_NAME AND E.SEX = D.SEX The original SQL as specified for SYSTEM R also had a CONTAINS comparison operator, which is used in conjunction with nested correlated queries This operator was dropped from the language, possibly because of the difficulty in implementing it efficiently

19. Slide 5-19 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 CORRELATED NESTED QUERIES (cont.) Most implementations of SQL do not have this operator The CONTAINS operator compares two sets of values, and returns TRUE if one set contains all values in the other set (reminiscent of the division operation of algebra). Query 3: Retrieve the name of each employee who works on all the projects controlled by department number 5. Q3:SELECT FNAME, LNAME FROMEMPLOYEE WHERE ( (SELECTPNO FROMWORKS_ON WHERESSN=ESSN) CONTAINS (SELECTPNUMBER FROMPROJECT WHEREDNUM=5) )

20. Slide 5-20 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 CORRELATED NESTED QUERIES (cont.) In Q3, the second nested query, which is not correlated with the outer query, retrieves the project numbers of all projects controlled by department 5 The first nested query, which is correlated, retrieves the project numbers on which the employee works, which is different for each employee tuple because of the correlation

21. Slide 5-21 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 THE EXISTS FUNCTION EXISTS is used to check whether the result of a correlated nested query is empty (contains no tuples) or not We can formulate Query 12 in an alternative form that uses EXISTS as Q12B below EXISTS AND NOT EXISTS are usually used in conjunction with a correlated nested query

22. Slide 5-22 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 THE EXISTS FUNCTION (cont.) Query 12: Retrieve the name of each employee who has a dependent with the same first name and same sex as the employee. Q12B: SELECT FNAME, LNAME FROMEMPLOYEEE WHEREEXISTS (SELECT* FROMDEPENDENT WHERESSN=ESSN AND FNAME=DEPENDENT_NAME AND E.SEX = SEX )

23. Slide 5-23 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 THE EXISTS FUNCTION (cont.) Query 6: Retrieve the names of employees who have no dependents. Q6:SELECT FNAME, LNAME FROMEMPLOYEE WHERENOT EXISTS (SELECT* FROM DEPENDENT WHERE SSN=ESSN) In Q6, the correlated nested query retrieves all DEPENDENT tuples related to an EMPLOYEE tuple. If none exist, the EMPLOYEE tuple is selected

24. Slide 5-24 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 THE EXISTS FUNCTION (cont.) Query 7:List the names of managers who have at least one dependent. SELECT FNAME, LNAME FROMEMPLOYEE WHERE EXISTS (SELECT * FROM DEPENDENT WHERE SSN=ESSN) AND EXISTS (SELECT * FROM DEPARTMENT WHERE SSN = MGRSSN); The first nested query select all DEPENDENT tuples related to an EMPLOYEE The second nested query select all DEPARTMENT tuples managed by the EMPLOYEE If at least one of the first and at least one of the second exists, we select the EMPLOYEE tuple. Can you rewrite that query using only one nested query or no nested query ?

25. Slide 5-25 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 THE EXISTS FUNCTION (cont.) Query 3: Retrieve the name of each employee who works on all the projects controlled by department number 5 Can be used: (S1 CONTAINS S2) that logically equivalent to (S2 EXCEPT S1) is empty. SELECT FNAME, LNAME FROMEMPLOYEE WHERE NOT EXISTS ( (SELECT PNUMBER FROM PROJECT WHERE DNUM=5) EXCEPT (SELECT PNO FROM WORKS_ON WHERE SSN = ESSN)); The first subquery select all projects controlled by dept 5 The second subquery select all projects that particular employee being considered works on. If the set difference of the first subquery MINUS (EXCEPT) the second subquery is empty, it means that the employee works on all the projects and is hence selected

26. Slide 5-26 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 EXPLICIT SETS It is also possible to use an explicit (enumerated) set of values in the WHERE- clause rather than a nested query Query 17: Retrieve the social security numbers of all employees who work on project number 1, 2, or 3. Q17:SELECT DISTINCT ESSN FROMWORKS_ON WHEREPNO IN (1, 2, 3)

27. Slide 5-27 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 RENAMING ATTRIBUTE In SQL, its possible to rename attribute that appears in the result of a query by adding the qualifier AS followed by the desired new name. Q8A: SELECT E.LNAME AS EMPLOYEE_NAME, S.LNAME AS SUPERVISOR_NAME FROM EMPLOYEE E, EMPLOYEE S WHERE E.SUPERSSN = S.SSN;

28. Slide 5-28 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 Joined Relations Feature in SQL2 Can specify a "joined relation" in the FROM- clause Looks like any other relation but is the result of a join Allows the user to specify different types of joins (regular "theta" JOIN, NATURAL JOIN, LEFT OUTER JOIN, RIGHT OUTER JOIN, CROSS JOIN, etc)

29. Slide 5-29 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 Example-Cross Join Beers namemanf Beer 1XYZ Beer 2ABC Beer 3ABC Likes drinkerbeer NarpatiBeer 1 NizarBeer 1 DanuBeer 3 SELECT * FROM Beers CROSS JOIN Likes namemanfdrinkerBeer Beer 1XYZNarpatiBeer 1 XYZNizarBeer 1 XYZDanuBeer 3 Beer 2ABCNarpatiBeer 1 Beer 2ABCNizarBeer 1 Beer 2ABCDanuBeer 3 ABCNarpatiBeer 1 Beer 3ABCNizarBeer 1 Beer 3ABCDanuBeer 3

30. Slide 5-30 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 Example-Natural Join Likes drinkerbeer NarpatiBeer 1 NizarBeer 1 DanuBeer 3 HarithBeer 2 Frequents drinkerbar AviABC DanuXYZ NizarABC JackZanz SELECT * FROM Beers NATURAL JOIN Likes drinkerbeerbar NizarBeer 1ABC DanuBeer 3XYZ

31. Slide 5-31 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 Example-Theta Join Beers namemanf Beer 1XYZ Beer 2ABC Beer 3ABC Likes drinkerbeer NarpatiBeer 1 NizarBeer 1 DanuBeer 3 SELECT * FROM Beers B JOIN Likes L ON B.name = L.beer namemanfdrinkerbeer Beer 1XYZNarpatiBeer 1 XYZNizarBeer 1 Beer 3ABCDanuBeer 3

32. Slide 5-32 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 Example-Outer Join Beers namemanf Beer 1XYZ Beer 2ABC Beer 3ABC Likes SELECT * FROM Beers B LEFT OUTER JOIN Likes L ON B.name = L.beer namemanfdrinkerbeer Beer 1XYZNarpatiBeer 1 XYZNizarBeer 1 Beer 2ABC Beer 3ABCDanuBeer 3 drinkerbeer NarpatiBeer 1 NizarBeer 1 DanuBeer 3 AviBeer 5 SELECT * FROM Beers B RIGHT OUTER JOIN Likes L ON B.name = L.beer namemanfdrinkerbeer Beer 1XYZNarpatiBeer 1 XYZNizarBeer 1 Beer 3ABCDanuBeer 3 AviBeer 5

33. Slide 5-33 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 Example-Outer Join Beers namemanf Beer 1XYZ Beer 2ABC Beer 3ABC Likes SELECT * FROM Beers B FULL OUTER JOIN Likes L ON B.name = L.beer namemanfdrinkerbeer Beer 1XYZNarpatiBeer 1 XYZNizarBeer 1 Beer 2ABC Beer 3ABCDanuBeer 3 AviBeer 5 drinkerbeer NarpatiBeer 1 NizarBeer 1 DanuBeer 3 AviBeer 5

34. Slide 5-34 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 AGGREGATE FUNCTIONS Include COUNT, SUM, MAX, MIN, and AVG Query : Find the maximum salary, the minimum salary, and the average salary among all employees. SELECT MAX(SALARY), MIN(SALARY), AVG(SALARY) FROMEMPLOYEE Some SQL implementations may not allow more than one function in the SELECT-clause

35. Slide 5-35 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 AGGREGATE FUNCTIONS (cont.) Query : Find the maximum salary, the minimum salary, and the average salary among employees who work for the 'Research' department. SELECT MAX(SALARY), MIN(SALARY), AVG(SALARY) FROMEMPLOYEE, DEPARTMENT WHEREDNO=DNUMBER AND DNAME='Research'

36. Slide 5-36 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 AGGREGATE FUNCTIONS (cont.) Queries : Retrieve the total number of employees in the company (QA), and the number of employees in the 'Research' department (QB). QA:SELECT COUNT (*) FROMEMPLOYEE QB:SELECT COUNT (*) FROMEMPLOYEE,DEPARTMENT WHEREDNO=DNUMBER AND DNAME='Research’

37. Slide 5-37 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 GROUPING In many cases, we want to apply the aggregate functions to subgroups of tuples in a relation Each subgroup of tuples consists of the set of tuples that have the same value for the grouping attribute(s) The function is applied to each subgroup independently SQL has a GROUP BY-clause for specifying the grouping attributes, which must also appear in the SELECT-clause

38. Slide 5-38 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 GROUPING (cont.) Query 24: For each department, retrieve the department number, the number of employees in the department, and their average salary. Q24:SELECT DNO, COUNT (*), AVG (SALARY) FROMEMPLOYEE GROUP BYDNO In Q24, the EMPLOYEE tuples are divided into groups--each group having the same value for the grouping attribute DNO The COUNT and AVG functions are applied to each such group of tuples separately The SELECT-clause includes only the grouping attribute and the functions to be applied on each group of tuples A join condition can be used in conjunction with grouping

39. Slide 5-39 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 GROUPING (cont.) Query 25: For each project, retrieve the project number, project name, and the number of employees who work on that project. Q25:SELECT PNUMBER, PNAME, COUNT (*) FROMPROJECT, WORKS_ON WHEREPNUMBER=PNO GROUP BYPNUMBER, PNAME In this case, the grouping and functions are applied after the joining of the two relations

40. Slide 5-40 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 THE HAVING-CLAUSE Sometimes we want to retrieve the values of these functions for only those groups that satisfy certain conditions The HAVING-clause is used for specifying a selection condition on groups (rather than on individual tuples)

41. Slide 5-41 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 THE HAVING-CLAUSE (cont.) Query 26: For each project on which more than two employees work, retrieve the project number, project name, and the number of employees who work on that project. Q26: SELECT PNUMBER, PNAME, COUNT (*) FROMPROJECT, WORKS_ON WHEREPNUMBER=PNO GROUP BYPNUMBER, PNAME HAVINGCOUNT (*) > 2

42. Slide 5-42 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 Summary of SQL Queries A query in SQL can consist of up to six clauses, but only the first two, SELECT and FROM, are mandatory. The clauses are specified in the following order: SELECT FROM [WHERE ] [GROUP BY ] [HAVING ] [ORDER BY ]

43. Slide 5-43 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Revised by IB & SAM, Fasilkom UI, 2005 Summary of SQL Queries (cont.) The SELECT-clause lists the attributes or functions to be retrieved The FROM-clause specifies all relations (or aliases) needed in the query but not those needed in nested queries The WHERE-clause specifies the conditions for selection and join of tuples from the relations specified in the FROM-clause GROUP BY specifies grouping attributes HAVING specifies a condition for selection of groups ORDER BY specifies an order for displaying the result of a query A query is evaluated by first applying the WHERE-clause, then GROUP BY and HAVING, and finally the SELECT-clause