1. Advanced SQL (part 2) and SQL in practice CS263 Lecture 8

2. Ensuring transaction integrity User-defined transactions can improve system performance because transaction will be processed as sets rather than individually Some SQL systems have concurrency controls that handle the updating of a shared database by concurrent users These can journalise database changes, so that a database can be recovered after abnormal termination in the middle of a transaction Such controls are transparent to the user, no special programming is needed to ensure proper control of concurrent access to data

3. Data dictionary facilities Data dictionary = system tables that store metadata Users usually can view some of these tables, using SELECT statements that can generate reports about system usage, user privileges etc, Users are restricted from updating them, sine the DBMS maintains them and depends on them for its processing In Oracle there are over 100 data dictionary views Tables that anyone can access begin with USER or ALL Tables that only the Database Administrator can use begin with DBA

4. Data dictionary facilities –Examples: –DBA_TABLES – descriptions of all tables in database –DBA_CONSTRAINTS – description of constraints –DBA_USERS – information about the users of the system –DBA_TAB_PRIVS – descriptions of grants on objects in the database

5. SQL-99 enhancements/extensions Enhancements to SQL have been built into many implementations (including Oracle) User-defined data types (UDT) subclasses of standard types or an object type Analytical functions (for OLAP/Data visualisation) - many mathematical/statistical and related functions Persistent Stored Modules (SQL/PSM) - capability to create and drop code modules. Persistent means that a module of code will be stored until dropped, making it available for execution across user sessions.

6. SQL-99 enhancements/extensions –New statements: CASE, IF, LOOP, FOR, WHILE, REPEAT etc New statements and PSM introduce procedurality into SQL (statements are processed sequentially) whereas base SQL is a non-procedural language and no statement execution sequence is implied SQL-99 Standard not widely adopted yet Oracle has propriety version called PL/SQL

7. Routines and triggers These are stored in the database and controlled by the DBMSThese are stored in the database and controlled by the DBMS This promotes stronger data integrity and consistency of use within the databaseThis promotes stronger data integrity and consistency of use within the database Since they are stored once, code maintenance is simplifiedSince they are stored once, code maintenance is simplified Both consist of blocks of procedural codeBoth consist of blocks of procedural code Trigger code is stored in the database and runs automatically whenever the triggering event (such as an UPDATE) occursTrigger code is stored in the database and runs automatically whenever the triggering event (such as an UPDATE) occurs Routines do not run automatically, they have to be called in to operateRoutines do not run automatically, they have to be called in to operate

8. Triggers Since triggers are stored and executed in the database, they execute against all applications that access the database Triggers can also cascade, causing other triggers to fire They can be used to ensure referential integrity, enforce business rules, create audit trails etc. Constraints can be thought of as a special case of triggers, as they are applied automatically as a result of data modification commands (though they are not as flexible as triggers) Triggers have 3 parts, the event, the condition and the action The following trigger will automatically insert the order number whenever a new order is added

9. Triggers BIR stands for Before Insert Row, also requires that a sequence ID_SEQUENCE has been previously defined CREATE TRIGGER ORDER_ID_BIR BEFORE INSERT ON ORDER_T FOR EACH ROW BEGIN SELECT ID_SEQUENCE.NEXTVAL INTO: NEW.ORDER_ID FROM DUAL; END ORDER_ID_BIR;

10. Triggers Triggers may occur either before or after the statement that aroused the trigger is executed They may occur on INSERT, UPDATE or DELETE commands They may fire once for each time a row is affected, or they may fire once per statement Care should be taken when using them, since they fire automatically the user will be unaware of them One trigger can cause another to fire, can easily end up with an endless loop of triggers

11. Routines Routines are Program modules that execute on demand Functions – routines that return values and take input parameters Procedures – routines that do not return values and can take input or output parameters

12. Routines - example procedure CREATE OR REPLACE PROCEDURE PRODUCT_LINE_SALE AS BEGIN UPDATE PRODUCT_T SET SALE_PRICE = 0.90*STANDARD_PRICE WHERE STANDARD_PRICE >= 400; UPDATE PRODUCT_T SET SALE_PRICE = 0.85*STANDARD_PRICE WHERE STANDARD_PRICE < 400; END (To run this procedure we would use: EXEC PRODUCT_LINE_SALE)

13. Triggers contrasted with routines Procedures are called explicitly Triggers are event-driven

14. Oracle PL/SQL trigger syntax SQL-99 Create routine syntax

15. Embedded and dynamic SQL Embedded SQL - including hard-coded SQL statements in a program written in another language such as C or Java = more efficient processing than interactive SQL Dynamic SQL - ability for an application program to generate SQL code on the fly, as the application is running - central to many internet applications (discussed in a later lecture)

16. SQL in practice Following material illustrates moving from ER diagram to SQL code Following Fig. Shows a simple ER diagram Other slides show how to populate and query tables using SQL code

17. Identify entities and attributes Emp Dept EmpNo Salary Comm Hire Date Name Job DeptNo Location Name

18. Identify relationships Emp Manage Managed by Dept Works in Assigned Each employee may be managed by one other employee Each employee may manage one or more other employees Each employee must work in a single department Each department may be assigned one or more employees Integrity Rules – derived from ER Diagram:

19. Create a relational schema Emp (EmpNo, Name, Job, Sal, Comm, HireDate, Mgr, DeptNo) Dept (DeptNo, Name, Location) DeptNoNumber(2) NameVarchar2(14) LocationVarchar2(13) EmpNoNumber(4) NameVarchar2(10) JobVarchar2(9) SalNumber(7,2) CommNumber(7,2) HireDateDate MgrNumber(4) DeptNoNumber(2) Emp Dept

20. Create relational tables To create a relation in SQL the following ‘Create Table’ command is required: create table R (A 1 D 1, A 2 D 2, … A n D n, integrity constraint 1, integrity constarint 2 ) Where:R = Relation (table) name A = Attribute name D = Attribute domain create table Dept (deptno number(2), name varchar2(14), location varchar2(13), constraint DeptPK primary key (deptno)); create table Emp (empno number(4), name varchar2(10), job varchar2(9), sal number(7,2), comm number(7,2), hiredate date, mgr number(4), deptno number(2), constraint EmpPK primary key (empno), constraint EmpFK1 foreign key (mgr) references Emp, constraint EmpFK2 foreign key (deptno) references Dept);

21. Populate relational tables To create a tuple in SQL the following ‘Insert’ command is required: insert into R (attribute 1, attribute 2, … attribute n ) values (value 1, value 2, … value n ) insert into Emp ( empno, name, job, sal, comm, hiredate, mgr, deptno ) values (7839, ‘King’, ‘President’, 5000, NULL, ‘17-Nov-81’, NULL, 10) insert into Emp ( empno, name, job, sal, comm, hiredate, mgr, deptno ) values (7698, ‘Blake’, ‘Manager’, 1600, NULL, ’01-May-81’, 7839, 30) insert into Dept ( deptno, name, location ) values (10, ‘Accounting’, ‘New York’) insert into Dept ( deptno, name, location ) values (30, ‘Sales’, ‘Chicago) The insert order matters in terms of referential integrity constraints!

22. Query relational tables To query a relation in SQL the following ‘Select’ command is required: SELECT [ ALL | DISTINCT ] attribute 1, attribute 2, … attribute n FROM relation 1, relation 2, … relation n [ WHERE condition-expression ] [ GROUP BY attribute 1, attribute 2, … attribute n ] [ HAVING condition-expression ] [ ORDER BY attribute 1, attribute 2, … attribute n ] Simple Example: list all Employees and the departments they work in select empno, name, deptno from Emp; 7839King10 7698Blake30

23. Query relational tables Simple Example: list all Employees that work in department 30 select empno, name from Emp where deptno = 30; 7698Blake Simple Example: list all Employees that work in either department 10 or 30 select empno, name from Emp where deptno = 10 or deptno = 30; 7839King 7698Blake

24. Query relational tables - Join Example: list Employee and Department names of all employees that work in either department 10 or 30 select emp.name, dept.name from Emp, Dept where (emp.deptno = 10 or emp.deptno = 30); KingAccounting KingSales BlakeAccounting BlakeSales select emp.name, dept.name from Emp, Dept where (emp.deptno = dept.deptno) and (emp.deptno = 10 or emp.deptno = 30) KingAccounting BlakeSales

25. Query relational tables – Order by select emp.name, dept.name from Emp, Dept where (emp.deptno = dept.deptno) and (emp.deptno = 10 or emp.deptno = 30) order by emp.name asc; BlakeSales KingAccounting select emp.name, dept.name from Emp, Dept where (emp.deptno = dept.deptno) and (emp.deptno = 10 or emp.deptno = 30) order by dept.name desc; BlakeSales KingAccounting select name from Dept order by name; Accounting Sales Remember in relations neither tuples nor attributes have any intrinsic order!

26. Example relations EMPNONAME JOB MGR HIREDATE SAL COMM DEPTNO 7369 SMITH CLERK 7902 17-DEC-80 800 20 7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30 7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30 7566 JONES MANAGER 7839 02-APR-81 2975 20 7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30 7698 BLAKE MANAGER 7839 01-MAY-81 2850 30 7782 CLARK MANAGER 7839 09-JUN-81 2450 10 7788 SCOTT ANALYST 7566 19-APR-87 3000 20 7839 KING PRESIDENT 17-NOV-81 5000 10 7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30 7876 ADAMS CLERK 7788 23-MAY-87 1100 20 7900 JAMES CLERK 7698 03-DEC-81 950 30 7902 FORD ANALYST 7566 03-DEC-81 3000 20 7934 MILLER CLERK 7782 23-JAN-82 1300 10 DEPTNO NAMELOCATION 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON Dept Emp

27. Query relational tables - Outer Join Example: list all departments and the names of staff that work in them. select dept.name, emp.name from Emp, Dept where (emp.deptno (+) = dept.deptno) order by dept.name, emp.name ; Accounting Clark Accounting King Accounting Miller Operations Research Adams Research Ford Research Jones Research Scott Research Smith Sales Allen Sales Blake Sales James Sales Martin Sales Turner Sales Ward

28. Query relational tables – Group by Example: List employee’s departments giving a count of employees in each. select deptno from Emp order by deptno; 10 20 30 select deptno from Emp group by deptno; 10 20 30 select deptno, count(*) from Emp group by deptno; 10 3 20 5 30 6 Aggregate Function! Select queries can contain functions and calculations as well as attribute names in the select condition!

29. Query relational tables – Group by select deptno, sum(sal), sum(sal)/count(*) from Emp group by deptno; As we are dealing with groups of tuples, rather than individual tuples, there are only certain types of data that can be selected: 1) attributes named in the group by clause; 2) group aggregate functions; 3) expressions involving combinations of 1) and 2). 10 8750 2916.6667 20 10875 2175 30 9400 1566.6667 select deptno, count(*) from Emp group by deptno having count(*) > 4; 20 5 30 6 Example: List employee’s departments giving a count of employees in each, provided that there are over four employees in the department. The having clause is used in Group Selections in the same way that the where clause is used in standard tuple selections.

30. Query relational tables – Group by 10 8750 2916.6667 20 10875 2175 select deptno, sum(sal), sum(sal)/count(*) from Emp group by deptno having sum(sal)/count(*) > 2000 order by sum(sal)/count(*) desc; Combined Example: List, in reverse order of average department salary, the total salary and average salary for each department that has employees, and where the average salary of each department is over £2000 The result of an SQL Select is, as shown, a new (unnamed) relation. The attributes of this new relation are named on the basis of the select statement. DEPTNO SUM(SAL) SUM(SAL)/COUNT(*) 10 8750 2916.6667 20 10875 2175 DEPTNO Total Salary Avg Salary 10 8750 2916.6667 20 10875 2175 ALIAS ALIAS:- select deptno, sum(sal) “Total Salary”, sum(sal)/count(*) “Avg Salary”

31. Query relational tables – Inner Selects As the result of an SQL Select on a relation(s) is itself a relation, it follows that, as with Relational Algebra, the result of one select can be used as the input into another SQL Select! However, rather than create, and name, a separate relation to contain the output of the first select and then use this relation in the second select, it is possible to ‘pipe’ the output of the first select directly into the second select! select name, sal from Emp where sal > (select AVG(sal) from Emp) order by name; Example: List employee’s who earn more than the average company salary. NAME SAL BLAKE 2850 CLARK 2450 FORD 3000 JONES 2975 KING 5000 SCOTT 3000 2 1 2073.2143, is substituted for this select statement

32. Query relational tables – Inner Selects Remember: Inner Selects (also called sub-selects or sub-queries) are full- bodied SQL Select statements: Therefore, they can, when required to do so, return more than a single value (one tuple, one attribute) relation. Example: List employees who earn the maximum salary in each of the departments. select name, deptno, sal from Emp where (deptno, sal) in (select deptno, max(sal) from emp group by deptno) order by deptno; NAME DEPT SAL KING 10 5000 SCOTT 20 3000 FORD 20 3000 BLAKE 30 2850 DEPT MAX(SAL) 10 5000 20 3000 30 2850 This relation is substituted for the inner select statement

33. Query relational tables – Inner Selects Note: It is sometimes necessary to make reference to an attribute value from the outer select, within the Where Clause of the inner select. This can be achieved by using a Relation Alias! Example: List employee’s who earn more than the average salary in the department they work in. select name, deptno, sal from Emp E1 where sal > (select AVG(sal) from Emp where deptno = E1.deptno group by deptno) order by deptno; NAME DEPT SAL KING 10 5000 JONES 20 2975 SCOTT 20 3000 FORD 20 3000 ALLEN 30 1600 BLAKE 30 2850 The deptno attribute value of the current tuple will be substituted here! If there are 14 employee tuples there will be 14 separate substitutions (even though there are only three departments)! Relation Alias

34. Example: list all staff that work in either of two departments (each dept. has a separate database), showing their staff number, and date of birth. select staffno, dob from DepA UNION select staffno, dob from DepB; SQL set operations – Union staffnodob SL1014-02-64 SA5121-11-82 DS4001-01-40 staffnodob CC1511-03-66 SA5121-11-82  DepA DepB staffnodob SL1014-02-64 SA5121-11-82 DS4001-01-40 CC1511-03-66

35. Example: list all staff that work in both departments (each dept. has a separate database), showing their staff number, and date of birth. select staffno, dob from DepA INTERSECT select staffno, dob from DepB; SQL set operations – Intersection staffnodob SL1014-02-64 SA5121-11-82 DS4001-01-40 staffnodob CC1511-03-66 SA5121-11-82 DepA DepB  staffnodob SA5121-11-82

36. Example: list all staff that only work in department A (each dept. has a separate database), showing their staff number, and date of birth. select staffno, dob from DepA MINUS select staffno, dob from DepB; SQL set operations – difference staffnodob SL1014-02-64 SA5121-11-82 DS4001-01-40 staffnodob CC1511-03-66 SA5121-11-82 DepA DepB staffnodob SL1014-02-64 DS4001-01-40

37. SQL - Group Insert statement To create a set of tuples in SQL the following ‘Insert’ command can be used: insert into R (attribute 1, attribute 2, … attribute n ) select (attribute 1, attribute 2, … attribute n ) from relation 1, relation 2, … relation n [where condition-expression] [group by attribute 1, attribute 2, … attribute n ] [having condition-expression] [order by attribute 1, attribute 2, … attribute n ] insert into DepA (staffno, name, job, hiredate) select empno, name, job, hiredate from Emp where deptno = 10; Example: copy details of all employees that work in department 10 from the Emp relation into the DepA relation. corresponding attributes have to be of the same type Each tuple to be inserted has to be unique!

38. SQL - Delete statement delete from R [where condition-expression] To delete a set of tuples in SQL the following ‘Delete’ command is used: Example: remove details of all employees that work in department 10 from the Emp relation. Delete from Emp where deptno = 10; If the where clause is omitted then all tuples in the relation will be removed!

39. SQL - Update statement To alter a set of tuples in SQL the following ‘Update’ command is used: update R set attribute 1 = datavalue 1, attribute 2 = datavalue 2,... attribute n = datavalue n [where condition-expression] Example: increase the salary of all employees that work in department 10 by 10%. update Emp set sal = sal *1.1 where deptno = 10; If the where clause is omitted then all tuples in the relation will be altered!