PLSQL Tutorial

PL/SQL TUTORIAL
Doan Quang MinhApril
10, 2012 CTI Cosatech VN

About this slide
This Oracle PL/SQL tutorial guides you the
basics of programming in PL/SQL with appropriate
examples. You can use this tutorial as your
reference while programming with PL/SQL.
You should have basic knowledge about SQL
and database management before reading this.
2

Agenda
I. Introduction (5 minutes)
II. Basic syntax (15 minutes)
III. Advanced syntax (30 minutes)
IV. Conclusion (2 minutes)
V. Reference (2 minutes)
VI. Keywords (3 minutes)
VII. Q&A
3

I. Introduction
1. Introduction to PL/SQL
 What is PL/SQL?
 The PL/SQL Engine
2. Advantages of PL/SQL
 Block Structures
 Procedural Language Capability
 Better Performance
 Error Handling
4

1. Introduction to PL/SQL
What is PL/SQL?
 Procedural Language extension of SQL.
 PL/SQL is a combination of SQL along with the
procedural features of programming languages. It
was developed by Oracle Corporation in the early
90’s to enhance the capabilities of SQL.
5
I. Introduction

1. Introduction to PL/SQL(cont)
The PL/SQL Engine
 Oracle uses a PL/SQL engine to processes the
PL/SQL statements.
 A PL/SQL code can be stored in the client system
(client-side) or in the database (server-side).
6
I. Introduction

2. Advantages of PL/SQL
 Block Structures: PL SQL consists of blocks of
code, which can be nested within each other. Each
block forms a unit of a task or a logical module.
PL/SQL Blocks can be stored in the database and
reused.
 Procedural Language Capability: PL SQL consists
of procedural language constructs such as
conditional statements (if else statements) and
loops like (FOR loops).
7
I. Introduction

2. Advantages of PL/SQL(cont)
 Better Performance: PL SQL engine processes
multiple SQL statements simultaneously as a single
block, thereby reducing network traffic.
 Error Handling: PL/SQL handles errors or
exceptions effectively during the execution of a
PL/SQL program. Once an exception is
caught, specific actions can be taken depending
upon the type of the exception or it can be displayed
to the user with a message.
8
I. Introduction

II. Basic syntax
1. Block Structures
2. Operators
3. Comments
4. Delimiters
5. Variables
6. Constants
7. Records
8. Conditional Statements
9. Iterative Statements
9

1. Block Structures
 Basic block
[DECLARE]
Variable declaration
BEGIN
Program Execution
[EXCEPTION]
Exception handling
END;
10
II. Basic syntax
 Example
SET SERVEROUTPUT ON SIZE 1000000
BEGIN
dbms_output.put_line('Hello PL/SQL');
END;

2. Operators
 Comparison operators
NOT IS NULL LIKE BETWEEN IN AND OR
+ - * / @ ; = <> != || <= >=
 Assignment operator
:= (You can assign values to a variable, literal value, or function call
but NOT a table column)
11
II. Basic syntax

3. Comments
 Comment
-- comment
/* comment */
 Example
DECLARE
/* Multi-line comments are not required to actually use
multiple lines. */
BEGIN
-- This is a single line comment
NULL;
END;
12
II. Basic syntax

4. Delimiters
 Delimiter
Item separator .
Character string delimiter '
Quoted String delimiter "
Bind variable indicator :
Attribute indicator %
Statement terminator ;
 Example
job_record.jobname := 'Test Job';
v_empno emp.empno%TYPE := &empno;
13
II. Basic syntax

5. Variables
 Variable
variable_name datatype [NOT NULL := value ];
 Example
DECLARE
v_first_name VARCHAR2(20);
v_employee_id NUMBER NOT NULL;
v_last_name EMPLOYEES.LAST_NAME%TYPE;
v_employee EMPLOYEES%ROWTYPE;
v_hire_date DATE;
BEGIN
NULL;
END;
14
II. Basic syntax

6. Constants
 Constant
constant_name CONSTANT datatype := VALUE;
 Example
DECLARE
c_boss CONSTANT VARCHAR2(4) := ‘BOSS’;
BEGIN
NULL;
END;
15
II. Basic syntax

7. Records
 Record
TYPE record_type_name IS RECORD(
first_col_name column_datatype,
second_col_name column_datatype, ...);
record_name record_type_name;
 Example
DECLARE
TYPE employee IS RECORD(
v_employee_id NUMBER NOT NULL
,v_first_name VARCHAR2(20));
v_employee employee;
BEGIN
NULL;
END;
16
II. Basic syntax

8. Conditional Statements
 If statement
IF condition THEN
statement 1;
ELSE
statement 2;
END IF;
17
II. Basic syntax
 Example
IF v_employee.sal > 0 THEN
v_employee.sal := 1;
ELSE
v_employee.sal := 0;
END IF;

9. Iterative Statements
 Iterative statement
LOOP
statements;
EXIT WHEN condition; (EXIT;)
END LOOP;
WHILE <condition>
LOOP statements;
END LOOP;
FOR counter IN val1..val2
LOOP statements;
END LOOP;
18
II. Basic syntax
 Example
LOOP
monthly_val := daily_val * 31;
EXIT WHEN monthly_value > 4000;
END LOOP;
WHILE monthly_val <= 4000
LOOP monthly_val := daily_val * 31;
END LOOP;
FOR counter IN 1..9
LOOP monthly_val := daily_val * 31;
END LOOP;

III. Advanced syntax
1. Cursors
2. Explicit Cursors
3. Procedures
4. Functions
5. Parameters-Procedure, Function
6. Exception Handling
7. Triggers
19

1. Cursors
 What is cursor ?
 In memory work area
 Store rows selected from DB
 Process one row per time only
 Active set is the set of rows the cursor hold.
 Supported attributes
 %FOUND
 %NOTFOUND
 %ROWCOUNT
 %ISOPEN
20
III. Advanced

1. Cursors(cont)
 Two types of cursors in PL/SQL
 Implicit cursors
 Explicit cursors
 Implicit cursors
These are created by default when DML statements
like, INSERT, UPDATE, and DELETE statements are
executed. They are also created when a SELECT statement
that returns just one row is executed.
21
III. Advanced

1. Cursors(cont)
 Example
DECLARE
v_rows number(5);
BEGIN
UPDATE employee
SET salary = salary + 1000;
IF SQL%NOTFOUND THEN
dbms_output.put_line('None of the salaries where updated');
ELSIF SQL%FOUND THEN
v_rows := SQL%ROWCOUNT;
dbms_output.put_line('Salaries for ' || v_rows || 'employees are
updated');
END IF;
END;
22
III. Advanced

2. Explicit Cursors
 What is explicit cursor ?
An explicit cursor is defined in the declaration section of the PL/SQL
Block. It is created on a SELECT Statement which returns more than one row.
We can provide a suitable name for the cursor.
 How to use explicit cursors ?
 DECLARE the cursor in the declaration section.
 OPEN the cursor in the Execution Section.
 FETCH the data from cursor into PL/SQL variables or records in the
Execution Section.
 CLOSE the cursor in the Execution Section before you end the PL/SQL
Block.
23
III. Advanced

2. Explicit Cursors
 Example
 Declaring a cursor
DECLARE
CURSOR emp_cur IS
SELECT *
FROM emp_tbl
WHERE salary > 5000;
24
III. Advanced
 Accessing the cursor
BEGIN
OPEN emp_cur;
FETCH emp_cur INTO v_record;
process_one_record(v_record);
CLOSE emp_cur;
END;

3. Procedures
 What is procedures ?
 A named PL/SQL block
 A procedure has a header and a body
 May or may not return values
 If stored on DBMS, we call it stored procedures
25
III. Advanced

3. Procedures(cont)
 Declaration
CREATE [OR REPLACE] PROCEDURE proc_name [list of parameters]
IS
Declaration section
BEGIN
Execution section
EXCEPTION
Exception section
END;
 Execution
 From the SQL prompt : EXECUTE [or EXEC]
procedure_name;
 Within another procedure: procedure_name;
26
III. Advanced

3. Procedures(cont)
 Example
CREATE OR REPLACE PROCEDURE employer_details IS
CURSOR emp_cur IS
SELECT first_name, last_name, salary
FROM emp_tbl;
emp_rec emp_cur%ROWTYPE;
BEGIN
FOR emp_rec IN sales_cur
LOOP
dbms_output.put_line(emp_cur.first_name);
END LOOP;
END;
EXECUTE employer_details;
27
III. Advanced

4. Functions
 What is functions?
 A named PL/SQL block
 A function has a header and a body
 Must always return a value (different to a procedure)
 If stored on DBMS, we call it stored functions
28
III. Advanced

4. Functions(cont)
 Declaration
CREATE [OR REPLACE] FUNCTION function_name [parameters]
RETURN return_datatype;
IS Declaration_section
BEGIN
Execution_section
Return return_variable;
EXCEPTION
exception section
Return return_variable;
END;
29
III. Advanced

4. Functions(cont)
 Execution
 Since a function returns a value we can assign it to a variable
variable_name := function_name;
 As a part of a SELECT statement
SELECT function_name FROM table;
 In a PL/SQL Statements like,
dbms_output.put_line(function_name);
30
III. Advanced

4. Functions(cont)
 Example
CREATE OR REPLACE FUNCTION employer_details_func
RETURN VARCHAR(20);
IS
emp_name VARCHAR(20);
BEGIN
SELECT first_name INTO emp_name
FROM emp_tbl
WHERE empID = '100';
RETURN emp_name;
END;
SELECT employer_details_func FROM dual;
31
III. Advanced

5. Parameters in Procedure,
Functions
 3 ways to pass parameters
 IN-parameters
 OUT-parameters
 IN OUT-parameters
NOTE: If a parameter is not explicitly defined a parameter type, then
by default it is an IN type parameter.
32
III. Advanced

5. Parameters in
Procedure, Functions
 Example
CREATE OR REPLACE PROCEDURE emp_name (
p_id IN NUMBER
, p_emp_name OUT VARCHAR2(20))
IS
BEGIN
SELECT first_name INTO p_emp_name
FROM emp_tbl WHERE empID = p_id;
END;
33
III. Advanced

34
III. Advanced
 What is a exception handling?
 A feature to handle the Exceptions which occur in a PL/SQL
Block
 Avoid the source code from exiting abruptly
 When an exception occurs a messages which explains its
cause is received
 3 parts of an PL/SQL exception?
• Type of Exception
• An Error Code
• A message

35
III. Advanced
 Structure of Exception Handling
EXCEPTION
WHEN ex_name1 THEN
-- Error handling statements
WHEN ex_name2 THEN
WHEN Others THEN

36
III. Advanced
 3 types of exception
 Named System Exceptions
 Unnamed System Exceptions
 User-defined Exceptions

37
III. Advanced
 Example
BEGIN
-- Execution section
EXCEPTION
WHEN NO_DATA_FOUND THEN
dbms_output.put_line ('A SELECT...INTO did not return any
row.');
END;

7. Triggers
 What is a Trigger?
A trigger is a pl/sql block structure which is fired when a DML
statements like Insert, Delete, Update is executed on a database
table. A trigger is triggered automatically when an associated
DML statement is executed.
38
III. Advanced

7. Triggers(cont)
 How to create a trigger?
CREATE [OR REPLACE ] TRIGGER trigger_name
{BEFORE | AFTER | INSTEAD OF }
{INSERT [OR] | UPDATE [OR] | DELETE}
[OF col_name]
ON table_name
[REFERENCING OLD AS o NEW AS n]
[FOR EACH ROW]
WHEN (condition)
BEGIN
--- sql statements
END;
39
III. Advanced

7. Triggers(cont)
 Example
The price of a product changes constantly. It is important to
maintain the history of the prices of the products.
We can create a trigger to update the 'product_price_history' table
when the price of the product is updated in the 'product' table.
1. Create the 'product' table and 'product_price_history' table
40
III. Advanced
CREATE TABLE product_price_history
(product_id NUMBER(5)
,product_name VARCHAR2(32)
,supplier_name VARCHAR2(32)
,unit_price NUMBER(7,2) );
CREATE TABLE product
(product_id NUMBER(5)
,product_name VARCHAR2(32)
,supplier_name VARCHAR2(32)
,unit_price NUMBER(7,2) );

7. Triggers(cont)
 Example(cont)
2. Create the price_history_trigger and execute it.
41
III. Advanced
CREATE OR REPLACE TRIGGER price_history_trigger
BEFORE UPDATE OF unit_price
ON product
FOR EACH ROW
BEGIN
INSERT INTO product_price_history
VALUES
(:old.product_id,
:old.product_name,
:old.supplier_name,
:old.unit_price);
END;

7. Triggers(cont)
 Example(cont)
3. Lets update the price of a product.
-- Once executed, the trigger fires and updates the
-- product_price_history' table
UPDATE PRODUCT SET unit_price = 800 WHERE product_id = 100
4. If you ROLLBACK the transaction before committing to the database, the data
inserted to the table is also rolled back.
42
III. Advanced

7. Triggers(cont)
 Types of PL/SQL Triggers
 Row level trigger - An event is triggered for each row updated, inserted or
deleted
 Statement level trigger - An event is triggered for each SQL statement
executed
 PL/SQL Trigger Execution Hierarchy
 BEFORE statement trigger fires first
 Next BEFORE row level trigger fires, once for each row affected
 Then AFTER row level trigger fires once for each affected row. This events
will alternates between BEFORE and AFTER row level triggers
 Finally the AFTER statement level trigger fires
43
III. Advanced

7. Triggers(cont)
 How To know Information about Triggers.
 We can use the data dictionary view 'USER_TRIGGERS' to obtain
information about any trigger.
DESC USER_TRIGGERS;
 This view stores information about header and body of the trigger
SELECT * FROM user_triggers WHERE trigger_name =
'trigger_name';
 You can drop a trigger using the following command.
DROP TRIGGER trigger_name;
44
III. Advanced

IV. Conclusion
45
Now, I hope this slide gave you some ideas about working with PL/SQL.
Please let me know if there’s any mistake or issue in the tutorial. All
comments are welcome.
With our position in CTI Vietnam. This amount of knowledge would not be
enough for us. There’re many more topics we need to invest our time:
performance tuning, data mining, coding convention, best practices, …
So, let’s share our knowledge, TOGETHER.

V. Reference
46
1. PL/SQL Tutorial from plsql-tutorial.com
2. PL/SQL User's Guide and Reference, Release 2 (9.2), from
Oracle
3. Database Interaction with PL/SQL, Jagadish Chatarji (Dev
Shed)
4. PL/SQL Code Examples, ACS department, University of
Utah
5. Doing SQL from PL/SQL: Best and Worst Practices, Oracle

VI. Keywords
47
Below is some keywords not mentioned in this slide. If possible, you should
google them.
General: Embedded SQL, Native dynamic SQL, The DBMS_Sql API,
Name resolution, PL/SQL compiler, bounded and unbounded, oracle
hint, materialized view.
Cursors: sharable SQL structure, session cursor, ref cursor, cursor
variable, strong ref cursor, weak ref cursor, identified cursor, DBMS_Sql
numeric cursor.
Exception Handling: RAISE_APPLICATION_ERROR, PRAGMA,
EXCEPTION_INIT.
Triggers: CYCLIC CASCADING, ROLLBACK, INSTEAD OF,
REFERENCING OLD.

VII. Q&A
48
Questions, please
...

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