Introduction to PL/SQL

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

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

About PL/SQL

PL/SQL: Provides a block structure for executable units of

code. Maintenance of code is made easier with such a well-defined 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

PL/SQL Environment

PL/SQL engine

Oracle database server

SQL statement executor

Procedural statement executor

procedural

SQL

PL/SQLblock

Benefits of PL/SQL Integration of procedural constructs with SQL Improved performance

SQLIF...THEN

SQLELSE

SQLEND IF;SQL

SQL 1

SQL 2…

Benefits of PL/SQL

Modularized program development Integration with Oracle tools Portability Exception handling

PL/SQL Block Structure

DECLARE (optional) Variables, cursors, user-defined exceptions

BEGIN (mandatory) SQL statements PL/SQL statements

EXCEPTION (optional) Actions to perform

when errors occur END; (mandatory)

Block Types

Anonymous Procedure Function

[DECLARE]

BEGIN --statements

[EXCEPTION]

END;

PROCEDURE nameIS

BEGIN --statements

[EXCEPTION]

END;

FUNCTION nameRETURN datatypeISBEGIN --statements RETURN value;[EXCEPTION]

END;

Program Constructs

Application triggers

Application packages

Application proceduresor functions

Anonymous blocks

Tools Constructs

Object types

Database triggers

Stored packages

Stored procedures orfunctions

Anonymous blocks

Database ServerConstructs

Object types

Create an Anonymous Block

Enter the anonymous block in the SQL Developer workspace:

Execute an Anonymous Block

Click the Run Script button to execute the anonymous block:

Run Script

Test the Output of a PL/SQL Block

Enable output in SQL Developer by clicking the Enable DBMS Output button on the DBMS Output tab:

Use a predefined Oracle package and its procedure: DBMS_OUTPUT.PUT_LINE

DBMS_OUTPUT.PUT_LINE(' The First Name of the Employee is ' || f_name);…

Enable DBMS Output

DBMS Output Tab

Test the Output of a PL/SQL Block

Declaring PL/SQL Variables

Objectives

After completing this lesson, you should be able to do the following: Recognize valid and invalid identifiers List the uses of variables Declare and initialize variables List and describe various data types Identify the benefits of using the %TYPE attribute Declare, use, and print bind variables

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_deptnoFROM …

v_fname

v_deptno

Jennifer

10

Requirements for Variable Names

A variable name: Must start with a letter Can include letters or numbers Can include special characters (such as $, _, and # ) Must contain no more than 30 characters Must not include reserved words

Handling Variables in PL/SQL Variables are:

Declared and initialized in the declarative section Used and assigned new values in the executable

section Passed as parameters to PL/SQL subprograms Used to hold the output of a PL/SQL subprogram

Declaring and Initializing PL/SQL Variables

Syntax:

Examples:

identifier [CONSTANT] datatype [NOT NULL] [:= | DEFAULT expr];

DECLARE v_hiredate DATE; v_deptno NUMBER(2) NOT NULL := 10; v_location VARCHAR2(13) := 'Atlanta'; c_comm CONSTANT NUMBER := 1400;

Declaring and Initializing PL/SQL Variables

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; /

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Delimiters in String Literals

DECLARE v_event VARCHAR2(15);BEGIN v_event := q'!Father's day!'; DBMS_OUTPUT.PUT_LINE('3rd Sunday in June is : '|| v_event ); v_event := q'[Mother's day]'; DBMS_OUTPUT.PUT_LINE('2nd Sunday in May is : '|| v_event );END;/

Types of Variables PL/SQL variables:

Scalar Composite Reference Large object (LOB)

Non-PL/SQL variables: Bind variables

TRUE

Types of Variables

25-JAN-01

Atlanta256120.08

Snow WhiteLong, long ago,

in a land far, far away, there lived a princess called

Snow White. . .

Guidelines for Declaring and InitializingPL/SQL Variables

Follow naming conventions. Use meaningful identifiers for variables. Initialize variables designated as NOT NULL and CONSTANT.

Initialize variables with the assignment operator (:=) or the DEFAULT keyword:

Declare one identifier per line for better readability and code maintenance.

v_myName VARCHAR2(20):='John';

v_myName VARCHAR2(20) DEFAULT 'John';

Guidelines for Declaring PL/SQL Variables

Avoid using column names as identifiers.

Use the NOT NULL constraint when the variable must hold a value.

DECLARE employee_id NUMBER(6);BEGIN SELECT employee_id INTO employee_id FROM employees WHERE last_name = 'Kochhar';END;/

Scalar Data Types Hold a single value Have no internal components

Atlanta

TRUE 25-JAN-01

256120.08

The soul of the lazy man desires, and he has nothing; but the soul of the diligent

shall be made rich.

Base Scalar Data Types

CHAR [(maximum_length)] VARCHAR2 (maximum_length) NUMBER [(precision, scale)] BINARY_INTEGER PLS_INTEGER BOOLEAN BINARY_FLOAT BINARY_DOUBLE

Base Scalar Data Types

DATE TIMESTAMP TIMESTAMP WITH TIME ZONE TIMESTAMP WITH LOCAL TIME ZONE INTERVAL YEAR TO MONTH INTERVAL DAY TO SECOND

Declaring Scalar Variables

Examples:DECLARE v_emp_job VARCHAR2(9); v_count_loop BINARY_INTEGER := 0; v_dept_total_sal NUMBER(9,2) := 0; v_orderdate DATE := SYSDATE + 7; c_tax_rate CONSTANT NUMBER(3,2) := 8.25; v_valid BOOLEAN NOT NULL := TRUE; ...

%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 The name of the declared variable

Declaring Variables with the %TYPE Attribute

Syntax

Examples... emp_lname employees.last_name%TYPE;...

identifier table.column_name%TYPE;

... balance NUMBER(7,2); min_balance balance%TYPE := 1000;...

Declaring Boolean Variables

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.

Bind Variables

Bind variables are: Created in the environment Also called host variables Created with the VARIABLE keyword Used in SQL statements and PL/SQL blocks Accessed even after the PL/SQL block is executed Referenced with a preceding colon

Printing Bind Variables

Example:

VARIABLE b_emp_salary NUMBERBEGIN SELECT salary INTO :b_emp_salary FROM employees WHERE employee_id = 178; END;/PRINT b_emp_salarySELECT first_name, last_name FROM employees WHERE salary=:b_emp_salary;

Printing Bind Variables

Example:VARIABLE b_emp_salary NUMBERSET AUTOPRINT ONDECLARE v_empno NUMBER(6):=&empno;BEGIN SELECT salary INTO :b_emp_salary FROM employees WHERE employee_id = v_empno; END;

7000

Output:

LOB Data Type Variables

Book(CLOB)

Photo(BLOB)

Movie(BFILE)

NCLOB

Composite Data Types

TRUE 23-DEC-98 ATLANTA

1 5000

2 2345

3 12

4 3456

1 SMITH

2 JONES

3 NANCY

4 TIM

PL/SQL table structure PL/SQL table structure

PLS_INTEGER

VARCHAR2

PLS_INTEGER

NUMBER

Writing Executable Statements

Objectives

After completing this lesson, you should be able to do the following: Identify lexical units in a PL/SQL block Use built-in SQL functions in PL/SQL Describe when implicit conversions take place and

when explicit conversions have to be dealt with Write nested blocks and qualify variables with

labels Write readable code with appropriate indentation Use sequences in PL/SQL expressions

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:

Identifiers: v_fname, c_percent Delimiters: ; , +, - Literals: John, 428, True Comments: --, /* */

PL/SQL Block Syntax and Guidelines Literals

Character and date literals must be enclosed in single quotation marks.

Numbers can be simple values or in scientific notation.

Statements can span several lines.name := 'Henderson';

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Commenting Code

Prefix single-line comments with two hyphens (--).

Place multiple-line comments 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;/

SQL Functions in PL/SQL

Available in procedural statements: Single-row functions

Not available in procedural statements: DECODE Group functions

SQL Functions in PL/SQL: Examples

Get the length of a string:

Get the number of months an employee has worked:

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_descriptionv_desc_size:= LENGTH(prod_description);

v_tenure:= MONTHS_BETWEEN (CURRENT_DATE, v_hiredate);

Using Sequences in PL/SQL Expressions

Starting in 11g:

Before 11g:

DECLARE v_new_id NUMBER;BEGIN SELECT my_seq.NEXTVAL INTO v_new_id FROM Dual;END;/

DECLARE v_new_id NUMBER;BEGIN v_new_id := my_seq.NEXTVAL;END;/

Data Type Conversion

Converts data to comparable data types Is of two types:

Implicit conversion Explicit conversion

Functions: TO_CHAR TO_DATE TO_NUMBER TO_TIMESTAMP

Data Type Conversion

date_of_joining DATE:= '02-Feb-2000';

date_of_joining DATE:= 'February 02,2000';

date_of_joining DATE:= TO_DATE('February 02,2000','Month DD, YYYY');

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Nested Blocks

PL/SQL blocks can be nested. An executable section (BEGIN … END) can contain nested blocks.

An exception section can contain nested blocks.

Nested Blocks

Example: DECLARE v_outer_variable VARCHAR2(20):='GLOBAL

VARIABLE'; BEGIN DECLARE v_inner_variable VARCHAR2(20):='LOCAL

VARIABLE'; BEGIN DBMS_OUTPUT.PUT_LINE(v_inner_variable); DBMS_OUTPUT.PUT_LINE(v_outer_variable); END; DBMS_OUTPUT.PUT_LINE(v_outer_variable); END;

Variable Scope and Visibility

DECLARE v_father_name VARCHAR2(20):='Patrick'; v_date_of_birth DATE:='20-Apr-1972'; BEGIN DECLARE v_child_name VARCHAR2(20):='Mike'; v_date_of_birth DATE:='12-Dec-2002'; BEGIN DBMS_OUTPUT.PUT_LINE('Father''s Name: '||v_father_name); DBMS_OUTPUT.PUT_LINE('Date of Birth: '||

v_date_of_birth); DBMS_OUTPUT.PUT_LINE('Child''s Name: '||v_child_name); END; DBMS_OUTPUT.PUT_LINE('Date of Birth: '||v_date_of_birth); END; /

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Qualify an Identifier

BEGIN <<outer>> DECLARE v_father_name VARCHAR2(20):='Patrick'; v_date_of_birth DATE:='20-Apr-1972'; BEGIN DECLARE v_child_name VARCHAR2(20):='Mike'; v_date_of_birth DATE:='12-Dec-2002'; BEGIN DBMS_OUTPUT.PUT_LINE('Father''s Name: '||v_father_name); DBMS_OUTPUT.PUT_LINE('Date of Birth: ' ||outer.v_date_of_birth); DBMS_OUTPUT.PUT_LINE('Child''s Name: '||v_child_name); DBMS_OUTPUT.PUT_LINE('Date of Birth: '||v_date_of_birth); END; END; END outer;

Quiz: Determining Variable Scope

BEGIN <<outer>>DECLARE v_sal NUMBER(7,2) := 60000; v_comm NUMBER(7,2) := v_sal * 0.20; v_message VARCHAR2(255) := ' eligible for commission';BEGIN DECLARE v_sal NUMBER(7,2) := 50000; v_comm NUMBER(7,2) := 0; v_total_comp NUMBER(7,2) := v_sal + v_comm; BEGIN v_message := 'CLERK not'||v_message; outer.v_comm := v_sal * 0.30; END; v_message := 'SALESMAN'||v_message;END;END outer;/

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Operators in PL/SQL Logical Arithmetic Concatenation Parentheses to control order

of operations

Exponential operator (**)

Same as in SQL}

Operators in PL/SQL: Examples

Increment the counter for a loop.

Set the value of a Boolean flag.

Validate whether an employee number contains a value.

loop_count := loop_count + 1;

good_sal := sal BETWEEN 50000 AND 150000;

valid := (empno IS NOT NULL);

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

Indenting Code

For clarity, indent each level of code.

BEGIN IF x=0 THEN y:=1; END IF;END;/

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;/

Interacting with the Oracle Database Server

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

SQL Statements in PL/SQL

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.

SELECT Statements in PL/SQL

Retrieve data from the database with a SELECT statement.

Syntax:

SELECT select_listINTO {variable_name[, variable_name]...

| record_name} FROM table[WHERE condition];

SELECT Statements in PL/SQL

The INTO clause is required. Queries must return only one row.

Example: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;/

Retrieving Data in PL/SQL Retrieve hire_date and salary for the

specified employee.

Example: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; END;/

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;

Retrieving Data in PL/SQL Return the sum of the salaries for all the

employees in the specified department. Example:

Naming Conventions

DECLARE hire_date employees.hire_date%TYPE; sysdate hire_date%TYPE; employee_id employees.employee_id%TYPE := 176;

BEGIN SELECT hire_date, sysdate INTO hire_date, sysdate FROM employees WHERE employee_id = employee_id; END; /

Naming Conventions

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.

Using PL/SQL to Manipulate Data

Make changes to database tables by using DML commands: INSERT UPDATE DELETE MERGE

INSERT

UPDATE

DELETE

MERGE

Inserting Data

Add new employee information to the EMPLOYEES table.

Example: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;/

Updating Data

Increase the salary of all employees who are stock clerks.

Example:DECLARE sal_increase employees.salary%TYPE := 800; BEGIN UPDATE employees SET salary = salary + sal_increase WHERE job_id = 'ST_CLERK';END;/

Deleting Data

Delete rows that belong to department 10 from the employees table.

Example:DECLARE deptno employees.department_id%TYPE := 10; BEGIN DELETE FROM employees WHERE department_id = deptno;END;/

Merging Rows

Insert or update rows in the copy_emp table to match the employees table.BEGIN

MERGE INTO copy_emp c USING employees e ON (e.employee_id = c.empno) WHEN MATCHED THEN UPDATE SET c.first_name = e.first_name, c.last_name = e.last_name, c.email = e.email, . . . WHEN NOT MATCHED THEN INSERT VALUES(e.employee_id, e.first_name, e.last_name, . . .,e.department_id);END;/

SQL Cursor

A cursor is a pointer to the private memory area allocated by the Oracle server.

A cursor is used to handle the result set of a SELECT statement.

There are two types of cursors: Implicit: Created and managed internally by the

Oracle server to process SQL statements Explicit: Declared explicitly by the programmer

SQL Cursor Attributes for Implicit Cursors Using SQL cursor attributes, you can test the

outcome of your SQL statements.

SQL%FOUND Boolean attribute that evaluates to TRUE if the most recent SQL statement

returned at least one row

SQL%NOTFOUND

Boolean attribute that evaluates to TRUE if

the most recent SQL statement did notreturn even one row

SQL%ROWCOUNT

An integer value that represents the number of rows affected by the most

recent SQL statement

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;