FEN  Queries: SELECT  Data Manipulation: INSERT, UPDATE, DELETE SQL: Structured Query Language – Part 2

2 VW: new database FEN Look at this database:..\lektion03 (SQL2)\vwDatabase.pdf..\lektion03 (SQL2)\vwDatabase.pdf Create the database. These scripts may be helpful.scripts

SQL: Data Manipulation Language SELECT UPDATE INSERT DELETE FEN All work on tables

Queries: SELECT Syntax: SELECT FROM [WHERE ] [GROUP BY ] [HAVING ] [ORDER BY ] [...]:WHERE, GROUP BY, HAVING and ORDER BY may be omitted. FEN

Examples: Company (Q0): Row and column selection: SELECTBdate, Address FROMEmployee WHEREFname= ’John’ AND Minit = ’B’ AND Lname = ’Smith’ All attributes: SELECT * --- FEN

Examples: Company (Q1): JOIN: SELECT Fname, Lname, Address FROMEmployee, Department WHEREDname = ’Research’ AND Dno = Dnumber Last term in the WHERE-clause is the join-condition. If omitted the result will be the Cartesian product. Alternative syntax is possible. FEN

Examples: Company (Q2): JOIN several tables: SELECTPnumber, Dnum, Lname, Address FROMProject, Employee, Department WHEREPlocation = ’Stafford’ AND Dnum = Dnumber AND Ssn = Mgrssn Note: Two join-conditions in the WHERE-clause. FEN

Examples: Company (Q8): Ambiguous attribute names and aliases: SELECTE.Fname, E.Lname, S.Fname, S.Lname FROMEmployee E, Employee S WHEREE.Superssn= S.Ssn Employee is joined with itself using the aliases E and S. ’.’ (”dot”)-notation may also be used to resolve ambiguous attribute Names (remember Minibank?). FEN

Examples: Company SQL-tables are NOT sets (in the mathematical sense of the word set): ( Q11):SELECT Salary FROM Employee (Q11A):SELECT DISTINCT Salary FROM Employee FEN

Examples: Company SQL-tables are NOT sets in general, but in set operations (UNION, INTERSECT and EXCEPT) they are: (SELECT PNUMBER FROM PROJECT, DEPARTMENT, EMPLOYEE WHERE LNAME = ’Smith’ AND DNUM = DNUMBER AND MGRSSN = SSN ) UNION (SELECT PNUMBER FROM PROJECT, WORKS_ON, EMPLOYEE WHERE LNAME = ’Smith’ AND PNO = PNUMBER AND ESSN = SSN) FEN

Updates i SQL: Updates: Inserting rows:INSERT Deleting rows:DELETE Updating row values:UPDATE As SELECT they work on tables. FEN

Examples: Company Inserting a single row: INSERT INTO EMPLOYEE VALUES (’Richard’,’K’,’Marini’,’ ’, ’30-DEC-52’,’98 Oak Forest, Katy, ’TX’,’M’,37000,’ ’,4) Inserting a single row, selected attributes: INSERT INTO EMPLOYEE(FNAME,LNAME,SSN) VALUES(’Richard’,’Marini’,’ ’) Is rejected if any of the other attributes is defined NOT NULL and doesn’t have defined a default value. FEN

Examples: Company Deleting rows: DELETE FROMEMPLOYEE WHERELNAME =’Brown’ DELETE FROMEMPLOYEE WHERESSN = ’ ’ DELETE FROMEMPLOYEE WHEREDNO IN (SELECTDNUMBER FROMDEPARTMENT WHEREDNAME = ’Research’) DELETE FROMEMPLOYEE (Not equivalent to: ´DROP TABLE EMPLOYEE’. Why not?) FEN

Examples: Company Updating rows: UPDATEPROJECT SETPLOCATION = ’Bellaire’, DNUM = 5 WHEREPNUMBER = 10 UPDATEEMPLOYEE SETSALARY = SALARY*1.1 WHEREDNO IN(SELECTDNUMBER FROMDEPARTMENT WHEREDNAME = ’Research’) Note, that it is only possible to affect one table in one UPDATE statement. FEN

Exercises 1.Try out some of the SQL queries on the previous slides. FEN

16 Company: Exercise FEN Do Exercise 2, phase 4 on CompanyExercise.pdf CompanyExercise.pdf

17 Exercise: VW-database FEN Look at this database:..\lektion03 (SQL2)\vwDatabase.pdf..\lektion03 (SQL2)\vwDatabase.pdf Do some of the queries in SQL