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Relational Operators, SQL, and Access Query

Relational Operators, SQL, and Access Query. ISYS 562. Relational Operators. Set operators: Union, intersection, difference, Cartesian product Relational operators: Selection, projection, join, etc. Union. Set1={A, B, C} Set2={C, D, E} Union: Members in Set 1 or in Set 2

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Relational Operators, SQL, and Access Query

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  1. Relational Operators, SQL, and Access Query ISYS 562

  2. Relational Operators • Set operators: Union, intersection, difference, Cartesian product • Relational operators: Selection, projection, join, etc.

  3. Union • Set1={A, B, C} • Set2={C, D, E} • Union: Members in Set 1 or in Set 2 • Set1 U Set 2 = {A, B, C, D, E} • Or

  4. Intersect • Members in Set 1 and in Set 2 • Set1 ∩ Set2={C} • And

  5. Difference • Set1 – Set2: Members in Set1 but not in set2 = {A,B} • Set2 – Set1:Members in Set2 but not in set1 = {D, E} • Set1-Set2 ≠ Set2 – Set1

  6. Use Union and Difference to Simulate Intersect • Set1 ∩ Set2 = Set1 – (Set1 – Set2)

  7. Files as Sets • Business students’ file: BusSt • Science student’s file: SciSt • BusSt U SciSt: • BusSt ∩ SciSt • BusSt – SciSt • Spring 04 Student file: S04St • Fall 04 Student file: F04St • S04St – F04St • F04St – S04St

  8. Product • Set1 = {a, b, c} • Set2 = {X, Y, Z} • Set1 X Set2 = {aX, aY aZ, bX, bY, bZ, cX, cY, cZ}

  9. Faculty File: • FID Fname • F1 Chao • F2 Smith • Student File: • SID Sname FID • S1 Peter F1 • S2 Paul F2 • S3 Smith F1 • Faculty X Student:

  10. Projection • Projection operation works on a single relation and defines a vertical subset of the relation, extracting the values of specified attributes.

  11. Duplications due to Projection • WorkLog file: • EID PjID Hours • E1 P2 5 • E1 P1 4 • E2 P2 6 • E2 P1 8 • E3 P1 4 • Project eid from (WorkLog) • Project Hours from (WorkLog) • In practice, users determine whether to eliminate duplicates: • SELECT DISTINCT EID FROM WorkLog; • SELECT HOURS FROM WorkLog WHERE PjID = ‘P1’;

  12. Natural Join • The two relations must have common attributes. • Combines two relations to form a new relation where records of the two relations are combined if the common attributes have the same value. One occurrence of each common attribute is eliminated.

  13. Aggregate Functions • Max, Min, Sum, Count, Avg • Aggregates by grouping fields

  14. Student: SID,Sname, GPA, Sex, Major • Enroll: SID, CID • Course: CID, Cname, Credits • Queries: • Number of students in each course • CID, CName, NumbeOfStudents • Total credits for each student: • SID, Sname, TotalCredits

  15. Outer Join • Records in a relation that do not have matching values are included in the result relation. Missing values are set to null.

  16. Outer Join Exmple • Product Table: • PID Pname • P1 TV • P2 VCR • P3 Computer • P4 Tape • P5 DVD • TotalSales • PID TotalSales • P1 50 • P3 60 • P5 40 • Product Join TotalSales • Product OuterJoin Totalsales

  17. Branch: BID City B1 SF B2 SM B3 SJ Full Outer Join: BID City PID B1 SF P3 B2 SM Null B3 SJ P2 Null LA P1 Right Outer Join: BID City PID B1 SF P3 B3 SJ P2 Null LA P1 Property: PID City P1 LA P2 SJ P3 SF Left Outer Join: BID City PID B1 SF P3 B2 SM Null B3 SJ P2

  18. Structured Query Language

  19. Language Overview • Two major components: • Data definition language • Create Table • Data manipulation language • Updating database: • Insert, Delete, Update • Query database: • Select

  20. CREATE TABLE • CREATE TABLE tableName(fields and data type separated by commas); • Ex. • CREATE TABLE employee( eid CHAR(5), ename VARCHAR(40), sex CHAR, salary NUMERIC(9,2), hire_Date DATE);

  21. SQL Insert Command INSERT INTO tableName VALUES (field values separated by commas); INSERT INTO tableName (Column names separated by commas)VALUES (field values separated by commas); Ex 1. Customer table with CID, CNAME, CITY, RATING. a. INSERT INTO CUSTOMER VALUES (‘C1’, ‘SMITH’, ‘SF’, ‘A’); b. INSERT INTO CUSTOMER (CID, CNAME,RATING) VALUES (‘C1’, ‘SMITH’, ‘A’);

  22. SQL Delete Command DELETE FROM tableName [WHERE criteria]; Ex 1. Delete a record from the Customer table. DELETE FROM CUSTOMER WHERE CID = ‘C1’;

  23. SQL Update Command UPDATE tableName SET field = new value [WHERE criteria]; Ex 1. UPDATE CUSTOMER SET RATING = ‘A’ WHERE CID=‘C1’; Ex 2. UPDATE CUSTOMER SET CITY = ‘SF’, SET RATING = ‘A’ WHERE CID=‘C1’;

  24. Selection • SELECT * FROM tableName WHERE criteria; • Criteria: • =, <>, <, >, <=, >= • (), NOT, AND, OR • BETWEEN • WHERE salary BETWEEN 1000 AND 10000; • LIKE, NOT LIKE: *, %, _ • WHERE ename LIKE “C*” • IN, NOT IN • WHERE eid IN (‘e1’,’e3’) • IS NULL • WHERE rating IS NULL

  25. Projection: • SELECT fields FROM tableName WHERE criteria; • SELECT DISTINCT fields FROM tableName WHERE criteria; • Field name alias: AS • Ex: SELECT eid AS empID, ename AS empName FROM emp; • Product: • SELECT fields FROM table1, table2; • table name alias: • Ex: SELECT s.*, f.* FROM student s, faculty f;

  26. Natural Join • SELECT * FROM table1 NATURAL JOIN table2; • SELECT * FROM student NATURAL JOIN faculty; • SELECT * FROM table1, table2 WHERE table1.JoinAttribute = table2.JoinAttribute; • SELECT * FROM student, faculty • WHERE student.fid = faculty.fid; • Table name alias: • SELECT * FROM student s, faculty f • WHERE s.fid = f.fid; • Other forms: • FROM student s JOIN faculty f ON s.fid=f.fid; • FROM student s INNER JOIN faculty f ON s.fid=f.fid; • FROM student JOIN faculty USING fid; • Not supported by Oracle

  27. Sorting • ORDER BY fieldName [DESC] • SELECT * FROM student ORDER BY sname; • SELECT * FROM student ORDER BY sname DESC; • More than one field: • SELECT * FROM student ORDER BY major, sname;

  28. Set Operators • Union compatible • (SELECT * FROM table1) • UNION (SELECT * FROM table2); • INTERSECT (SELECT * FROM table2); • MINUS (SELECT * FROM table2);

  29. Aggregates • SELECT AVG(fieldName) FROM tableName; • COUNT(fieldName), COUNT(*) • COUNT(DISTINCT fieldName) • MAX(fieldName) • MIN(fieldName) • SUM(fieldName) • More than one aggregate: • SELECT AVG(fieldName), MAX(fieldName), MIN(fieldName) FROM tableName; • With alias: • SELECT AVG(gpa) AS avggpa, COUNT(sid) AS scount • FROM student;

  30. GROUP BY • SELECT groupingField, function(fieldname) FROM tablename GROUP BY groupingField; • SELECT major, count(sid) FROM student GROUP BY major; • All field names in the GROUP BY clause must be included in the retrieved fields. • Compute the number of courses taken by each student: • SELECT sid, sname, COUNT(cid) • FROM student NATURAL JOIN enroll • GROUP BY sid, sname; • WHERE clause must come before the GROUP BY: • SELECT major, count(sid) FROM student WHERE GPA > 3.0 GROUP BY major;

  31. Adding a Criteria for the Sub Totals with HAVING • SELECT major, count(sid) FROM student • GROUP BY major • HAVING count(sid) > 5; • Sometime the aggregates are not required to display: • Find majors that have more than 5 students: • SELECT major FROM student • GROUP BY major • HAVING count(sid) > 5;

  32. Sub (or Nested ) Query • Q: Find students whose GPA is below the average. • The criteria itself required a SQL statement. • SELECT * FROM student • WHERE gpa < (SELECT AVG(gpa) FROM student);

  33. Sub Query with IN • Q: Find students who take at least one course and display their ID and name. • SELECT sid, sname FROM • student NATURAL JOIN enroll • GROUP BY sid • HAVING COUNT(cid) > 1; • SELECT sid, sname FROM student • WHERE sid IN (SELECT DISTINCT sid FROM enroll); • Q: Find students who take more than 5 courses and display their ID and name. • SELECT sid, sname FROM student • WHERE sid IN (SELECT sid FROM enroll GROUP BY sid • HAVING COUNT(cid) > 5);

  34. Sub Query with ALL/SOME/ANY • Q: Find students whose gpa is greater than all/some bus majors’ gpa: • SELECT sid, sname FROM student • WHERE gpa > ALL(SELECT gpa FROM student WHERE major=‘bus’); • SELECT sid, sname FROM student • WHERE gpa > SOME (SELECT gpa FROM student WHERE major=‘bus’); • SELECT sid, sname FROM student • WHERE gpa > ANY (SELECT gpa FROM student WHERE major=‘bus’);

  35. Access Query • Selection, Projection, Product, Join, Outer Join • Calculated field, alias, parameter query • GroupBy, Having • Union, Intersect, Minus • Wizards: CrossTab, Find Duplicates, Find Unmatched • Others: • Make table, update

  36. Examples • University database: • Student: SID, Sname, Sex, Major, GPA, FID • Account: SID, Balance • Faculty: FID, Fname • Course: CID, Cname, Credits • StudentCourse: SID, CID • Questions: • Display student names who owe at least 2000. • Display faculty names who advise at least one student • Display faculty names who do not advise any student • Display faculty names who advise more than 2 students • Display total credits for all students • Find students enrolled in 263 • Find students enrolled in 263 and 363

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