1. PL/SQL (1)

2. Learning Objectives In this chapter, you will learn:
About procedural SQL
About PL/SQL structure
How to declare variables in PL/SQL
About data types in PL/SQL
About conditional and iterative structure in PL/SQL
About cursors, how to create and use them

3. Introduction
Performs a conditional or looping operation by isolating critical code and making all application programs call the shared code
Yields better maintenance and logic control
Persistent stored module (PSM): Block of code containing:
Standard SQL statements
Procedural extensions that is stored and executed at the DBMS server
To remedy the lack of procedural functionality in SQL and to provide some standardization within the many vendor offerings, the SQL-99 standard defined the use of persistent stored modules.

4. What is PL/SQL Procedural Language SQL (PL/SQL)
An Oracle-specific programming language based on
SQL with procedural extensions designed to run inside the Oracle database.
Use and storage of procedural code and SQL statements within the database
Merging of SQL and traditional programming constructs
Procedural code is executed as a unit by DBMS when invoked by end user

5. PL/SQL Structure PL/SQL is an algorithmic, block-structured language.
PL/SQL groups its statements into units called BLOCKS which can be unnamed (anonymous) or named ( sub- programs)
PL/SQL blocks can contain only SQL DML commands ( SELECT, INSERT, UPDATE, and DELETE) and Transaction Commands which are COMMIT & ROLLBACK.
The use of data definition language (DDL) commands (Create, Alter, Drop, etc.) is not directly supported in a PL/SQL block.

6. PL/SQL Structure
The subprograms can be either – Functions, procedures, and they can be grouped into a packages.
PL/SQL also allows access to databases via Cursors, Triggers, stored procedures and functions.

7. PL/SQL Structure
A block has three parts: Declaration, Executable and Exception-handling. A block has the following structure.
DECLARE
Declarations -- Optional
BEGIN
  Executable -- Mandatory
EXCEPTION
  Exception-handling /* here you can specify the actions to execute when the program encounters a runtime error; it is optional */
END;
The three parts of a block are separated by the DECLARE, BEGIN, EXCEPTION, and END PL/SQL reserved words. You should not use any reserved word for any other than its designated purpose.

8. Declaration Part
Variables used to hold program data are declared in the Declaration part.
All declaration statements must be located between the DECLARATION and BEGIN reserved words.
The syntax of a variable declaration is:
identifier data_type;
The Declaration part is optional, but any variable used in Executable part must be declared; otherwise, the program will fail.
In addition to variable, you can also declare other program objects, such as Constant and Exception
A variable name must start with a letter; the rest can be letters, digits, or any of the following three symbols: _ (underscore), # (number sign), and $ (dollar sign).  The maximum length of a name is 30 characters. Additionally, PL/SQL is not case sensitive.
The following four variable names, for example, are not valid.
9code_var -- start with numeric
Name_var% -- has a % character
price var -- has a blank
Date_the_price_of_this_produce_was_changed_var --
longer than 30 characters

9. Data types and variables
all the sql data types
variables declaration:
<variable-name> <datatype> [not null] [:=<initial value>]
ex. sid number(5) not null := 1111;
sname varchar2(30);
grade number(5,2) := 2.5;
constants declaration:
<constant-name> constant <data-type> := <value>
ex. maxcolumns constant integer(2) := 30;

10. Table 8.9 - PL/SQL Basic Data Types

11. Anchor Variables: ROWTYPE and TYPE
The syntax of the ROWTYPE and TYPE datatypes syntaxes are respectively:
variable_name table_name%ROWTYPE;
variable_name table_name.column_name%TYPE;
You use ROWTYPE at once refer to all the columns of a table; while the TYPE refers to a specific column.
ex.
cnum customers.sid%type;
ctable customers%rowtype; -- creates a variable of type table that has the same fields as the customers table;

12. Storing Data in Variables (SELECT INTO)
The SELECT INTO clause of SQL is used to retrieve data from one or more database tables and place the returned data into predefined variables.

13. IF…THEN…ELSIF … ELSE … END IF
Control Structures
Control Structures
Conditional
Statements
Iterative Statements
IF….. THEN…..END IF
LOOP … END LOOP
IF…THEN…ELSE… END IF
WHILE … LOOP …. END LOOP
IF…THEN…ELSIF … ELSE … END IF
FOR … LOOP … END LOOP

14. Conditional Statements
Actions are triggered based on the result of conditions

15. Conditional statements
The syntax of the Simple CASE statement is.
Note:
Selector should be of simple type
CASE selector
WHEN selector_value_1 THEN statements_1
WHEN selector_value_2 THEN statements_2
WHEN ...
[ ELSE else_statements ]
END CASE;

16. Iterative statements
Loops repeat an instruction or a set of instructions multiple times.
Three types of loops: basic loop, For Loop and While Loop.
The EXIT instruction exits the loop
Basic Loop
LOOP Start of the Loop
instruction1 ; Instructions
. . .
EXIT [ WHEN condition ]; -- Exit the Loop
END LOOP ; End of the Loop

17. Basic Loop - Example
The following PL / SQL program displays multiples of 3, 4 and 5 which are between 4 and 32
DECLARE
i NUMBER(2) := 4;
BEGIN
LOOP
IF (MOD(i,3)=0) THEN
DBMS_OUTPUT.PUT_LINE (i || ‘ is a multiple of 3’);
END IF;
IF (MOD(i,4)=0) THEN
DBMS_OUTPUT.PUT_LINE (i || ‘ is a multiple of 4’);
IF (MOD(i,5)=0) THEN
DBMS_OUTPUT.PUT_LINE (i || ‘ is a multiple of 5’);
i := i+1;
EXIT WHEN i>32;
END LOOP;
END;

18. FOR Loop - Example
The following PL / SQL program calculates the factorial of 10 using For Loop.
DECLARE
fact_num NUMBER := 1;
BEGIN
FOR v_counter IN LOOP
fact_num := fact_num * v_counter;
END LOOP;
DBMS_OUTPUT.PUT_LINE('Factorial of 10 is: '||fact_num);
END;

19. While Loop - Example
The following PL / SQL program calculates the factorial of 10 using While Loop.
DECLARE
  n_counter   NUMBER := 10;
  n_factorial NUMBER := 1;
  n_temp      NUMBER;
BEGIN
  n_temp := n_counter;
  WHILE n_counter > 0
  LOOP
    n_factorial := n_factorial * n_counter;
    n_counter   := n_counter - 1;
  END LOOP;
  DBMS_OUTPUT.PUT_LINE('factorial of ' || n_temp ||     ' is ' || n_factorial);
END;

20. FOR LOOP WITH INSERT- Example
CREATE TABLE item(ItemNum NUMBER(2)); BEGIN FOR num IN 1..5 LOOP INSERT INTO item VALUES(num); END LOOP; END; / SELECT * FROM item;

21. PL/SQL Processing with Cursors
Oracle server uses work areas called Private SQL Zones to execute SQL statements and to store information being processed
You can use PL / SQL cursors to name a private SQL area and access the data it contains.
A memory area of fixed size containing the result of a query.
Used to interpret and analyze SQL statements.
Cursors
You can think of a cursor as a reserved area of memory in which the output of the query is stored, like an array holding columns and rows. Cursors are held in a reserved memory area in the DBMS server, not in the client computer.
Implicit:
generated and managed by ORACLE for each SQL statement
Explicit:
Declared by developers in the DECLARE section of a PL/SQL block

22. Explicit Cursors The use of an explicit cursor requires fours steps:
Declaration of the cursor in declare section
Opening the cursor in Begin section
Processing the cursor in Begin section
Closing the cursor in Begin or Exception section

23. Declaration of a cursor
Cursor’s declaration
Syntax:
Declare
Cursor <cusor_name> IS
SELECT col1, col2, col3, ….
FROM tab1, tab2, tab3, …
Where <Condition>; ….
Declaration of a cursor
Example:
Declare
Cursor c_employee IS SELECT empNo, empName, salary FROM employee
Where salary between 1000
AND 2500;

24. OPEN <cursor_name> ;
Cursor’s Opening
Opening the cursor realizes:
Allocation of the memory to the cursor
semantic and syntactic analysis of the SQL statement
It is only when the cursor is opened that the SQL query is executed
The cursor is opened in the Begin section of the block as follows:
OPEN <cursor_name> ;

25. Cursors’ processing
Cursor-style processing involves retrieving data from the cursor one row at a time
Current row is copied to PL/SQL variables
After the fetch, the “current” row pointer moves to the next row in the set and continues until it reaches the end of the cursor.

26. Table 8.10 - Cursor Processing Commands

27. Table 8.11 - Cursor Attributes

28. Cursor - Example END; END; CURSOR with FOR LOOP CURSOR with LOOP
DECLARE
  Cursor c_customers is
Select id, name, address
From customers;
cusRecord c_customers%rowtype;
BEGIN
   For cusRecord in c_customers Loop
    dbms_output.put_line (cusRecord .id||’’|| cusRecord .name||’’|| cusRecord.address);
  END LOOP;
 END;
DECLARE
  c_id customers.id%type;
  c_name customers.name%type;
c_addr customers.address%type;
Cursor c_customers is
Select id, name, address
From customers;
BEGIN
  Open c_customers;
  LOOP
   Fetch c_customers into c_id, c_name,
c_addr;
EXIT When c_customers%notfound;
dbms_output.put_line (c_id||’’||c_name||’’||c_addr);
  END LOOP;
Close c_customers;
 END;