Introduction to PL/SQL
Copyright © 2009, Oracle. All rights reserved.
Objectives
After completing this lesson, you should be able to do the
following:
• Explain the need for PL/SQL
• Explain the benefits of PL/SQL
• Identify the different types of PL/SQL blocks
• Output messages in PL/SQL
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Copyright © 2009, Oracle. All rights reserved.
About PL/SQL
PL/SQL:
• Stands for “Procedural Language extension to SQL”
• Is Oracle Corporation’s standard data access language for
relational databases
• Seamlessly integrates procedural constructs with SQL
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Copyright © 2009, Oracle. All rights reserved.
About PL/SQL
PL/SQL:
• Provides a block structure for executable units of code.
Maintenance of code is made easier with such a welldefined structure.
• Provides procedural constructs such as:
– Variables, constants, and data types
– Control structures such as conditional statements and loops
– Reusable program units that are written once and executed
many times
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Copyright © 2009, Oracle. All rights reserved.
PL/SQL Run-Time Architecture
PL/SQL block
procedural
PL/SQL
SQL
Procedural statement
executor
PL/SQL Engine
Oracle Server
SQL statement executor
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PL/SQL Block Structure
•
DECLARE (optional)
– Variables, cursors, user-defined exceptions
•
BEGIN (mandatory)
– SQL statements
– PL/SQL statements
•
EXCEPTION (optional)
– Actions to perform
when exceptions occur
•
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END; (mandatory)
Copyright © 2009, Oracle. All rights reserved.
Block Types
Procedure
Function
PROCEDURE name
IS
[DECLARE]
[EXCEPTION]
FUNCTION name
RETURN datatype
IS
BEGIN
--statements
RETURN value;
[EXCEPTION]
END;
END;
END;
BEGIN
--statements
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Copyright © 2009, Oracle. All rights reserved.
Anonymous
BEGIN
--statements
[EXCEPTION]
Examining an Anonymous Block
An anonymous block in the SQL Developer workspace:
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Executing an Anonymous Block
Click the Run Script button to execute the anonymous block:
Run Script (or F5)
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Agenda
•
•
•
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Understanding the benefits and structure of PL/SQL
Examining PL/SQL blocks
Generating output messages in PL/SQL
Copyright © 2009, Oracle. All rights reserved.
Enabling Output of a PL/SQL Block
1. To enable output in SQL Developer, execute the following
command before running the PL/SQL block:
SET SERVEROUTPUT ON
2. Use a predefined Oracle package and its procedure in the
anonymous block:
– DBMS_OUTPUT.PUT_LINE
DBMS_OUTPUT.PUT_LINE(' The First Name of the
Employee is ' || v_fname);
…
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Viewing the Output of a PL/SQL Block
Press F5 to execute the
command and PL/SQL
block.
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Declaring PL/SQL Variables
Copyright © 2009, Oracle. All rights reserved.
Use of Variables
Variables can be used for:
• Temporary storage of data
• Manipulation of stored values
• Reusability
SELECT
first_name,
department_id
INTO
v_fname,
v_deptno
FROM …
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Jennifer
Copyright © 2009, Oracle. All rights reserved.
10
v_fname
v_deptno
Requirements for Variable Names
A variable name:
• Must start with a letter
• Can include letters or numbers
• Can include special characters (such as $, _, and #)
•
•
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Must contain no more than 30 characters
Must not include reserved words
Copyright © 2009, Oracle. All rights reserved.
Declaring and Initializing PL/SQL Variables
Syntax:
identifier [CONSTANT] datatype [NOT NULL]
[:= | DEFAULT expr];
Examples:
DECLARE
v_hiredate
v_deptno
v_location
c_comm
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DATE;
NUMBER(2) NOT NULL := 10;
VARCHAR2(13) := 'Atlanta';
CONSTANT NUMBER := 1400;
Copyright © 2009, Oracle. All rights reserved.
Declaring and Initializing PL/SQL Variables
1
2
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DECLARE
v_myName VARCHAR2(20);
BEGIN
DBMS_OUTPUT.PUT_LINE('My name is: '|| v_myName);
v_myName := 'John';
DBMS_OUTPUT.PUT_LINE('My name is: '|| v_myName);
END;
/
DECLARE
v_myName VARCHAR2(20):= 'John';
BEGIN
v_myName := 'Steven';
DBMS_OUTPUT.PUT_LINE('My name is: '|| v_myName);
END;
/
Copyright © 2009, Oracle. All rights reserved.
Types of Variables
•
PL/SQL variables:
– Scalar (Basic)
– Boolean
– Large object (LOB)
– Composite (cursors, records , array)
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Copyright © 2009, Oracle. All rights reserved.
Types of Variables
15-JAN-09
TRUE/ FALSE
Snow White
Long, long ago,
in a land far, far away,
there lived a princess called
Snow White. . .
Atlanta
256120.08
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Copyright © 2009, Oracle. All rights reserved.
Guidelines for Declaring and Initializing
PL/SQL Variables
•
•
•
•
Follow consistent naming conventions.
Use meaningful identifiers for variables.
Initialize variables that are designated as NOT NULL and
CONSTANT.
Initialize variables with the assignment operator (:=) or the
DEFAULT keyword:
v_myName VARCHAR2(20):='John';
v_myName VARCHAR2(20) DEFAULT 'John';
•
Declare one identifier per line for better readability and
code maintenance.
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Copyright © 2009, Oracle. All rights reserved.
Guidelines for Declaring PL/SQL Variables
•
Avoid using column names as identifiers.
DECLARE
employee_id NUMBER(6);
BEGIN
SELECT
employee_id
INTO
employee_id
FROM
employees
WHERE
last_name = 'Kochhar';
END;
/
•
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Use the NOT NULL constraint when the variable must hold
a value.
Copyright © 2009, Oracle. All rights reserved.
Naming Conventions of PL/SQL
Structures Used in This Course
PL/SQL Structure
Convention
Example
Variable
v_variable_name
v_rate
Constant
c_constant_name
c_rate
Subprogram
parameter
p_parameter_name
p_id
Bind (host) variable
b_bind_name
b_salary
Cursor
c_cursor_name
cur_emp
Record
rec_record_name
rec_emp
Type
type_name_type
ename_table_type
Exception
e_exception_name
e_products_invalid
File handle
f_file_handle_name
f_file
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Copyright © 2009, Oracle. All rights reserved.
Scalar Data Types
•
•
Hold a single value
Have no internal components
TRUE
15-JAN-09
The soul of the lazy man
desires, and he has nothing;
but the soul of the diligent
shall be made rich.
256120.08
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Atlanta
Copyright © 2009, Oracle. All rights reserved.
Base Scalar Data Types
•
•
•
•
•
•
•
•
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CHAR [(maximum_length)]
VARCHAR (maximum_length)
NUMBER [(precision, scale)]
BINARY_INTEGER
PLS_INTEGER
BOOLEAN TRUE FALSE
BINARY_FLOAT
BINARY_DOUBLE
Copyright © 2009, Oracle. All rights reserved.
Base Scalar Data Types
•
•
•
•
•
•
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DATE
TIMESTAMP
TIMESTAMP WITH TIME ZONE
TIMESTAMP WITH LOCAL TIME ZONE
INTERVAL YEAR TO MONTH
INTERVAL DAY TO SECOND
Copyright © 2009, Oracle. All rights reserved.
Declaring Scalar Variables
Examples:
DECLARE
v_emp_job
v_count_loop
v_dept_total_sal
v_orderdate
c_tax_rate
v_valid
...
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VARCHAR2(9);
BINARY_INTEGER := 0;
NUMBER(9,2) := 0;
DATE := SYSDATE + 7;
CONSTANT NUMBER(3,2) := 8.25;
BOOLEAN NOT NULL := TRUE;
Copyright © 2009, Oracle. All rights reserved.
%TYPE Attribute
•
Is used to declare a variable according to:
– A database column definition
– Another declared variable
•
Is prefixed with:
– The database table and column name
– The name of the declared variable
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Copyright © 2009, Oracle. All rights reserved.
Declaring Variables
with the %TYPE Attribute
Syntax
identifier
table.column_name%TYPE;
Examples
...
v_emp_lname
...
employees.last_name%TYPE;
...
v_balance
v_min_balance
...
NUMBER(7,2);
v_balance%TYPE := 1000;
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Copyright © 2009, Oracle. All rights reserved.
Declaring Boolean Variables
•
•
•
•
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Only the TRUE, FALSE, and NULL values can be assigned
to a Boolean variable.
Conditional expressions use the logical operators AND and
OR, and the unary operator NOT to check the variable
values.
The variables always yield TRUE, FALSE, or NULL.
Arithmetic, character, and date expressions can be used to
return a Boolean value.
Copyright © 2009, Oracle. All rights reserved.
LOB Data Type Variables
Book
(CLOB)
Photo
(BLOB)
Movie
(BFILE)
NCLOB
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Composite Data Types: Records and Collections
V_comp_orddtl.orderdate
TRUE
23-DEC-98
ATLANTA
PL/SQL Collections:
1
2
3
4
SMITH
JONES
NANCY
TIM
1
2
3
4
5000
2345
12
3456
NUMBER
VARCHAR2
PLS_INTEGER
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PLS_INTEGER
Copyright © 2009, Oracle. All rights reserved.
Writing Executable Statements
Copyright © 2009, Oracle. All rights reserved.
Lexical Units in a PL/SQL Block
Lexical units:
• Are building blocks of any PL/SQL block
• Are sequences of characters including letters, numerals,
tabs, spaces, returns, and symbols
• Can be classified as:
–
–
–
–
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Identifiers: v_fname, c_percent
Delimiters: ; , +, Literals: John, 428, True
Comments: --, /* */
Copyright © 2009, Oracle. All rights reserved.
Commenting Code
•
•
Prefix single-line comments with two hyphens (--).
Place a block comment between the symbols /* and */.
Example:
DECLARE
...
v_annual_sal NUMBER (9,2);
BEGIN
/* Compute the annual salary based on the
monthly salary input from the user */
v_annual_sal := monthly_sal * 12;
--The following line displays the annual salary
DBMS_OUTPUT.PUT_LINE(v_annual_sal);
END;
/
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Copyright © 2009, Oracle. All rights reserved.
SQL Functions in PL/SQL
•
Available in procedural statements:
– Single-row functions
•
Not available in procedural statements:
– DECODE
– Group functions
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Copyright © 2009, Oracle. All rights reserved.
SQL Functions in PL/SQL: Examples
•
Get the length of a string:
v_desc_size INTEGER(5);
v_prod_description VARCHAR2(70):='You can use this
product with your radios for higher frequency';
-- get the length of the string in prod_description
v_desc_size:= LENGTH(v_prod_description);
•
Get the number of months an employee has worked:
v_tenure:= MONTHS_BETWEEN (CURRENT_DATE, v_hiredate);
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Copyright © 2009, Oracle. All rights reserved.
Programming Guidelines
Make code maintenance easier by:
• Documenting code with comments
• Developing a case convention for the code
• Developing naming conventions for identifiers and other
objects
• Enhancing readability by indenting
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Copyright © 2009, Oracle. All rights reserved.
Indenting Code
For clarity, indent each level of code.
BEGIN
IF x=0 THEN
y:=1;
END IF;
END;
/
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DECLARE
deptno
NUMBER(4);
location_id NUMBER(4);
BEGIN
SELECT department_id,
location_id
INTO
deptno,
location_id
FROM
departments
WHERE
department_name
= 'Sales';
...
END;
/
Copyright © 2009, Oracle. All rights reserved.
Interacting with Oracle Database Server:
SQL Statements in PL/SQL Programs
Copyright © 2009, Oracle. All rights reserved.
Objectives
After completing this lesson, you should be able to do the
following:
• Determine the SQL statements that can be directly
included in a PL/SQL executable block
• Manipulate data with DML statements in PL/SQL
• Use transaction control statements in PL/SQL
• Make use of the INTO clause to hold the values returned
by a SQL statement
• Differentiate between implicit cursors and explicit cursors
• Use SQL cursor attributes
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Copyright © 2009, Oracle. All rights reserved.
SQL Statements in PL/SQL
•
•
•
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Retrieve a row from the database by using the SELECT
command.
Make changes to rows in the database by using DML
commands.
Control a transaction with the COMMIT, ROLLBACK, or
SAVEPOINT command.
Copyright © 2009, Oracle. All rights reserved.
SELECT Statements in PL/SQL
Retrieve data from the database with a SELECT statement.
Syntax:
SELECT
INTO
FROM
[WHERE
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select_list
{variable_name[, variable_name]...
| record_name}
table
condition];
Copyright © 2009, Oracle. All rights reserved.
SELECT Statements in PL/SQL
•
The INTO clause is required.
•
Queries must return only one row.
DECLARE
v_fname VARCHAR2(25);
BEGIN
SELECT first_name INTO v_fname
FROM employees WHERE employee_id=200;
DBMS_OUTPUT.PUT_LINE(' First Name is : '||v_fname);
END;
/
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Copyright © 2009, Oracle. All rights reserved.
Retrieving Data in PL/SQL: Example
Retrieve hire_date and salary for the specified employee.
DECLARE
v_emp_hiredate
employees.hire_date%TYPE;
v_emp_salary
employees.salary%TYPE;
BEGIN
SELECT
hire_date, salary
INTO
v_emp_hiredate, v_emp_salary
FROM
employees
WHERE
employee_id = 100;
DBMS_OUTPUT.PUT_LINE ('Hire date is :'|| v_emp_hiredate);
DBMS_OUTPUT.PUT_LINE ('Salary is :'|| v_emp_ salary);
END;
/
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Copyright © 2009, Oracle. All rights reserved.
Retrieving Data in PL/SQL
Return the sum of salaries for all the employees in the specified
department.
Example:
DECLARE
v_sum_sal
NUMBER(10,2);
v_deptno
NUMBER NOT NULL := 60;
BEGIN
SELECT SUM(salary) -- group function
INTO v_sum_sal FROM employees
WHERE
department_id = v_deptno;
DBMS_OUTPUT.PUT_LINE ('The sum of salary is ' || v_sum_sal);
END;
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Copyright © 2009, Oracle. All rights reserved.
Naming Ambiguities
DECLARE
v_hire_date
employees.hire_date%TYPE;
v_sysdate
hire_date%TYPE;
v_employee_id
employees.employee_id%TYPE := 176;
BEGIN
SELECT
hire_date, sysdate
INTO
v_hire_date, v_sysdate
FROM
employees
WHERE
employee_id = employee_id;
END;
/
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Copyright © 2009, Oracle. All rights reserved.
Naming Conventions
•
•
•
•
•
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Use a naming convention to avoid ambiguity in the WHERE
clause.
Avoid using database column names as identifiers.
Syntax errors can arise because PL/SQL checks the
database first for a column in the table.
The names of local variables and formal parameters take
precedence over the names of database tables.
The names of database table columns take precedence
over the names of local variables.
Copyright © 2009, Oracle. All rights reserved.
Using PL/SQL to Manipulate Data
Make changes to database tables by using DML commands:
• INSERT
• UPDATE
• DELETE
DELETE
• MERGE
INSERT
UPDATE
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MERGE
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Inserting Data: Example
Add new employee information to the EMPLOYEES table.
BEGIN
INSERT INTO employees
(employee_id, first_name, last_name, email,
hire_date, job_id, salary)
VALUES(employees_seq.NEXTVAL, 'Ruth', 'Cores',
'RCORES',CURRENT_DATE, 'AD_ASST', 4000);
END;
/
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Updating Data: Example
Increase the salary of all employees who are stock clerks.
DECLARE
sal_increase
employees.salary%TYPE := 800;
BEGIN
UPDATE
employees
SET
salary = salary + sal_increase
WHERE
job_id = 'ST_CLERK';
END;
/
...
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Copyright © 2009, Oracle. All rights reserved.
Deleting Data: Example
Delete rows that belong to department 10 from the employees
table.
DECLARE
deptno
employees.department_id%TYPE := 10;
BEGIN
DELETE FROM
employees
WHERE department_id = deptno;
END;
/
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Copyright © 2009, Oracle. All rights reserved.
Agenda
•
•
•
1 - 52
Retrieving data with PL/SQL
Manipulating data with PL/SQL
Introducing SQL cursors
Copyright © 2009, Oracle. All rights reserved.
SQL Cursor
•
A cursor is a pointer to the private memory area allocated
by the Oracle Server. It is used to handle the result set of a
SELECT statement.
•
There are two types of cursors: implicit and explicit.
– Implicit: Created and managed internally by the Oracle
Server to process SQL statements
– Explicit: Declared explicitly by the programmer
Implicit cursor
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Explicit cursor
Copyright © 2009, Oracle. All rights reserved.
SQL Cursor Attributes for Implicit Cursors
Using SQL cursor attributes, you can test the outcome of your
SQL statements.
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SQL%FOUND
Boolean attribute that evaluates to TRUE if the
most recent SQL statement affected at least one
row
SQL%NOTFOUND
Boolean attribute that evaluates to TRUE if
the most recent SQL statement did not affect
even one row
SQL%ROWCOUNT
An integer value that represents the number of
rows affected by the most recent SQL statement
Copyright © 2009, Oracle. All rights reserved.
SQL Cursor Attributes for Implicit Cursors
Delete rows that have the specified employee ID from the
employees table. Print the number of rows deleted.
Example:
DECLARE
v_rows_deleted VARCHAR2(30)
v_empno employees.employee_id%TYPE := 176;
BEGIN
DELETE FROM employees
WHERE employee_id = v_empno;
v_rows_deleted := (SQL%ROWCOUNT ||
' row deleted.');
DBMS_OUTPUT.PUT_LINE (v_rows_deleted);
END;
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Copyright © 2009, Oracle. All rights reserved.
SQL%FOUND TRUE
SQL%NOTFOUND FALSE
SQL%ROWCOUNT 5
DECLARE
v_deptno number :=80;
BEGIN
-- from GUI accept department id and delete all employees in
that departments
-- but if number of records being deleted greater than 10
employees cancel the job
Copyright © 2009, Oracle. All rights reserved.
DELETE employees
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