1. Chapter 8
Advanced SQL
Pearson Education © 2009

2. Chapter 8 - Objectives How to use the SQL programming language
How to use SQL cursors
How to create stored procedures
How to create triggers
How to use triggers to enforce integrity constraints
Pearson Education © 2009

3. Chapter 8 – Objectives (continued)
The advantages and disadvantages of triggers
How to use recursive queries

4. The SQL Programming Language
Impedance mismatch
Mixing different programming paradigms
SQL is a declarative language
High-level language such as C is a procedural language
SQL and 3GLs use different models to represent data

5. The SQL Programming Language (continued)
SQL/PSM (Persistent Stored Modules)
PL/SQL (Procedural Language/SQL)
Oracle’s procedural extension to SQL
Two versions

6. Declarations
Variables and constant variables must be declared before they can be referenced
Possible to declare a variable as NOT NULL
%TYPE and %ROWTYPE

7. Declarations (continued)

8. Examples vRent NUMBER(6, 2) NOT NULL := 600;
vStaffNo Staff.staffNo%TYPE;

9. Assignments Variables can be assigned in three ways:
Using the normal assignment statement (:=)
SET
SQL SELECT or FETCH statement

10. Examples vX NUMBER; …. vStaffNo := ‘SG14’; vRent := 500;
SELECT COUNT(*) INTO vX
FROM PropertyForRent
WHERE staffNo = vStaffNo;
SET vStaffNo = ‘SG14’;

11. Control Statements Conditional IF statement Conditional CASE statement
Iteration statement (LOOP)
Iteration statement (WHILE and REPEAT)
Iteration statement (FOR)

12. IF Statement
IF ( vPosition = ‘Manager’) THEN vSalary := vSalary * 1.05; ELSIF (…) THEN //optional … ELSE //optional vSalary := vSalary * 1.08; END IF;

13. CASE Statement
CASE lowercase(input) WHEN ‘a’ THEN x := 1; WHEN ‘b’ THEN x := 2; y := 3; WHEN ‘default’ THEN x := 3; END CASE;

14. LOOP Statement
x := 1; myLoop: LOOP x := x+1; IF (x > 3) THEN EXIT myLoop; END IF; END LOOP myLoop; …

15. WHILE/REPEAT Statement
myLoop: x := 1; WHILE (x < 4) DO x := x+1; END WHILE myLoop; REPEAT UNTIL (x>3) END REPEAT myLoop;

16. FOR Statement
SELECT COUNT(*) INTO numberOfStaff FROM …. myLoop: FOR iStaff IN 1..numberOfStaff LOOP …. END LOOP myLoop;

17. Exceptions in PL/SQL Exception Identifier in PL/SQL
Raised during the execution of a block
Terminates block’s main body of actions
Exception handlers
Separate routines that handle raised exceptions
User-defined exception
Defined in the declarative part of a PL/SQL block

18. Example of Exception Handling in PL/SQL

19. Condition Handling Define a handler by Specifying its type
Exception and completion conditions it can resolve
Action it takes to do so
Handler is activated
When it is the most appropriate handler for the condition that has been raised by the SQL statement

20. Cursors in PL/SQL Cursor
Allows the rows of a query result to be accessed one at a time
Must be declared and opened before use
Must be closed to deactivate it after it is no longer required
Updating rows through a cursor

21. Using Cursors in PL/SQL to Process a Multirow Query

22. Cursor Flags %FOUND: true if the most recent fetch returns a row
%NOTFOUND: true if the most recent fetch returns no row
%ISOPEN: true if cursor is open
%ROWCOUNT: total number of rows returned so far

23. Cursor Parameter A cursor may be reused with parameter(s):
CURSOR propteryCursor(vStaffNo VARCHAR(4) ) IS
SELECT propertyNo, street, city, postcode
FROM PropertyForRent
WHERE staffNo = vStaffNo
ORDER BY propertyNo;
Later the cursor can be opened as:
OPEN propertyCursor(‘SG14’); …
OPEN propertyCursor(‘SA9’);

24. Updating Rows through a Cursor
A row may change after it has been fetched
Example:
CURSOR propterCursor IS
SELECT propertyNo, street, city, postcode
FROM PropertyForRent
WHERE staffNo = ‘SG14’
ORDER BY propertyNo
--Lock the PropertyForRent table immediately
FOR UPDATE NOWAIT;
Now in the loop:
UPDATE PropertyForRent
SET staffNo = ‘SG37’
WHERE CURRENT OF propertyCursor; …
COMMIT;

25. Subprograms, Stored Procedures, Functions, and Packages
Named PL/SQL blocks that can take parameters and be invoked
Types
Stored procedures: No return value
Functions: Always returns a single value
Parameters
IN: for input only. Default.
OUT: for output value only
IN OUT: for input and output

26. Procedure (in PL/SQL)
CREATE [OR REPLACE] PROCEDURE proc_name [list of parameters] {IS|AS} Declaration section BEGIN Execution section EXCEPTION Exception section END;

27. Example
CREATE PROCEDURE Get_emp_names (Dept_num IN NUMBER) IS Emp_name VARCHAR(10); CURSOR c1 (DepNo NUMBER) IS SELECT Ename FROM Emp_tab WHERE deptNo = DepNo; -- deptNo is an attribute BEGIN OPEN c1(Dept_num); LOOP FETCH c1 INTO Emp_name; EXIT WHEN c1%NOTFOUND; DBMS_OUTPUT.PUT_LINE(Emp_name); END LOOP; CLOSE c1; END;

28. Executing
In standalone statement:
EXECUTE procedure(parameter list);
Called from another PL/SQL block: …
procedure(parameter list);

29. Deleting
DROP PROCEDURE procedure-name;

30. Function
CREATE [OR REPLACE] FUNCTION function_name [ (parameter [,parameter]) ] RETURN return_datatype IS | AS [declaration_section] BEGIN executable_section [EXCEPTION exception_section] END [function_name];

31. Function Example
CREATE [OR REPLACE] FUNCTION FindCourse ( name_in IN VARCHAR2 ) RETURN NUMBER IS cnumber NUMBER; CURSOR c1 IS SELECT course_number FROM courses_tbl WHERE course_name = name_in; BEGIN open c1; fetch c1 into cnumber; … close c1; RETURN cnumber; END;

32. Example cont’d
SELECT course_name, FindCourse(course_name) AS course_id FROM courses WHERE subject = 'Mathematics';

33. Executing Similar to stored procedures
Pass the required parameters along with function name; If function returns a value, you can store returned value
Program control is transferred to the called function.
A called function performs defined task and when its return statement is executed or when it last end statement is reached, it returns program control back to the main program.

34. MS SQL Server Stored Procedure Example
To create:
CREATE PROCEDURE getAddress VARCHAR(30)) AS
BEGIN
SELECT * FROM Staff
WHERE City
END; GO
To Execute:
EXEC = ‘Houston’;

35. MS SQL Server Function Example
To create:
CREATE FUNCTION getSite INT )
RETURNS VARCHAR(50) AS
BEGIN
VARCHAR(50);
< 10
= ‘UHD.edu';
ELSE
= ‘Houston.gov';
END;
To execute:
SELECT dbo.getSite(8);

36. Triggers
Trigger
Defines an action that the database should take when some event occurs in the application
Format of a trigger
Types
TRIGGER Privilege
Advantages and disadvantages of triggers

37. Trigger Format

38. A BEFORE Trigger

39. An After Trigger
CREATE TRIGGER StaffAfterInsert AFTER INSERT ON Staff REFERENCEING NEW AS newrow FOR EACH ROW BEGIN INSERT INTO StaffAudit VALUES (:newrow.staffNo, :newrow.fName, :newrow.LName, :newrow.position, :newrow.sex, ….); END;

40. INSTEAD OF Trigger
Views are not updateable if there are more than two base tables
INSTEAD OF Triggers are used to update views

41. Trigger Privilege Must be the owner of the table
Or have been granted the TRIGGER privilege on the table

42. Trigger Advantages and Disadvantages
Reduce redundancy
Simply modifications
Increase security
Improve integrity
Improve processing power …
Performance overhead
Cascading effects