PLSQL Part1 Declaring Variables

8/8/2019 PLSQL Part1 Declaring Variables

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IBM SOLUTIONS DELIVERY INC.

2008 IBM Corporation

PL/SQL

Part 1 - Declaring Variables

Prepared by:

Sherwin O. Bautista


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Course Objectives

After completing this course, trainees should be able to do thefollowing:

Be on familiar terms with the basic PL/SQL block and its

sections Will be able to describe the significance of variables in PL/SQL Declare PL/SQL variables Execute a PL/SQL block


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DECLARE

{code .... }

BEGIN

{code.}

EXCEPTION

{code.}

END;

PL/SQL Block Structure

DECLARE - Optional

Variables, cursors,user-defined exceptions

BEGIN - Mandatory

-- SQL statements-- PL/SQL statements

EXCEPTION - Optional

Actions to perform when error occurs

END; - Mandatory

A PL/SQL block consists of up to three sections: declarative (optional), executable(required), and exception handling (optional).


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PL/SQL Block Structure

A PL/SQL block consists of up to three sections: declarative (optional), executable(required), and exception handling (optional).

Section Description Inclusion

Declarative Contains all variables, constants, cursors, and user-define exceptions that are

referenced in the executable and declarative sections

Optional

Executable Contains SQL statements to manipulate data in the database and PL/SQL statements

to manipulate data in the block

Mandatory

Exception

Handling

Specifies the actions to perform when errors and abnormal conditions arise in the

executable section

Optional


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Executing Statements and PL/SQL Blocks

Place a semicolon (;) at the end of a SQL statement or PL/SQL control statement

When the block is executed successfully, without unhandled errors or compile errors,the message output should be as follows:

PL/SQL procedure successfully completed.

Section keywords DECLARE, BEGIN, and EXCEPTION are not followed bysemicolons.

END and all other PL/SQL statements require a semicolon to terminate thestatement.

Note: Error is called an exception.


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[DECLARE]

BEGIN

-- statements

[EXCEPTION]

END;

Block Types

PROCEDUREnameIS

BEGIN

-- statements

[EXCEPTION]

END;

FUNCTIONnameRETURNdatatype

IS

BEGIN

-- statementsRETURNvalue;

EXCEPTION

END;

Anonymous Procedure Functions


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Block Types

Anonymous Blocks:

unnamed blocks

declared at the point in an application where they are to be executed

passed to the PL/SQL engine for execution at run time.

can be embed within a pre-compiler program and with in iSQL*Plus.

Subprograms: (declared as procedure or as functions)

named PL/SQL blocks that can accept parameters and can be invoked.

procedure use to perform an action

function to compute a value.

can store at the server or application level.

Note: A function is similar to a procedure, except a function must return a value.


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Program Construct

The program construct are available based on the environment in which they are executed.


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Use of Variables

Variable can be use for the following:

Temporary storage of data:

While validating data input and for processing later in the data flow process, datacan be temporarily stored.

Manipulation of stored values:

Variables can be used for calculations and other data manipulations withoutaccessing the database.

Reusability:

Once variables declared, variables can be used repeatedly in an applicationsimply by referencing them in the other statements.

Ease of maintenance:

When using %TYPE and %ROWTYPE, you declare variables, basing thedeclarations on the definitions of database columns. If definition changes, thevariable declaration changes accordingly at run time.


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Handling Variables in PL/SQL

Declare and Initialize Variables in the Declaration Section

Declaring variables in the declarative part of any PL/SQL block, subprograms, orpackage will allocate storage space for a value and can reference by specify its datatype, and name of storage location. A variable must declare before referencing it inother statements.

Assign New Values to Variables in the Executable Section

In the executable section, the existing value of the variable is replaced with the newvalue that is assigned to the variable.

Pass Values Into PL/SQLSubprograms through parameters

There are three parameter modes.

IN (default) -- use this parameter to pass values to the subprogram being

called.

OUT -- use this parameter to return values to the caller of a subprogram.

IN OUT -- use this parameter to pass initial values to the subprogram beingcalled and to return updated values to the caller.


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Types of Variables

PL/SQL supports four data type categories that can use for declaring variables, constant,and pointers.

Scalar-- hold a single value.

Composite-- records, allow group of fields to be defined and manipulated in PL/SQL blocks.

Reference-- hold values called pointer that designate other program items (note: notcovered in this course).

LOB (large objects)-- hold values called locators that specify the location of large objects (i.e. graphicimages) that are stored out of line.


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Types of Variables

TRUE represents a Boolean value.

08-AUG-08 represents a DATE

The photograph represents a BLOB

The text of a speech represents a LONG

75232.09 represents a NUMBER data type with precision and scale.

The movie represents a BFILE.

The city name EASTWOOD represents a VARCHAR2

Some illustration of variable data types:


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Declaring PL/SQL Variables

Examples:

Syntax:

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

DECLAREv_hiredate DATE;v_deptno NUMBER(2) NOT NULL := 10;v_location V ARCHAR2(13) := Eastwood;

v_comm CONSTANT NUMBER := 1400;


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Declaring PL/SQL Variables

In the syntax:

identifier is the name of the variable

CONSTANT constrains the variable so that its value cannot change;constants must be initialized.

data type is a scalar, composite, reference, orLOB data type.

NOT NULL constrains the variable so that it must contain a value.(NOT NULL variables must be initialized).

expr is any PL/SQL expression that can be a literal express or anothervariable or an expression involving operators and functions.

Syntax:

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


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Guidelines for Declaring PL/SQL Variables

Name the identifier according to the same rules used for SQL objects

Use naming conventions for example, v_name to represent a variable and c_name torepresent a constant variable.

Assign a value ifNOTNULL constraint is use.

Declare only one identifier per line (makes code easier to read and maintain).

In constant declarations, the keyword CONSTANT must precede the type specifier.

Example: v_sal CONSTANTREAL := 5000.00;

Initialize the variable to an expression with the assignment operator (:=) or, equivalent,with the DEFAULT reserved word.

Note: If you do not assign an initial value, the new variable contains NULL by defaultuntil you assign a value later.


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Naming Rules

Two variables can have the same name, provided they are in different blocks.

The variable name (identifier) should not be the same as the name of table columns usedin the block.

Correct

Example:

Wrong

DECLARE

employee_id NUMBER(6);BEGIN

SELECT employee_idINTO employee_idFROM employees

WHERE last_name = Cruz;END;

/

DECLARE

v_employee_id NUMBER(6);BEGIN

SELECT employee_idINTO v_employee_idFROM employees

WHERE last_name = Cruz;END;

/


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Variable Initialization and Keywords

Assignment operator (:=)

DEFAULT keyword

NOTNULL constraint

Syntax:

identifier := expr;

Examples:

v_hiredate := 28-JAN-2008;

v_lastname := Cruz;


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Variable Initialization and Keywords

In the Syntax:

identifier is the name of the scalar variable.

expr can be a variable, literal, or function callbut NOT a database column.

Note:

String literals must be enclosed in a single quotation marks.

For example: Hello,world.

If there is a single quotation mark in the string, use a single quotation mark twice.

For example:

the value is : FISHERMANS DRIVE

the string would be: FISHERMANS DRIVE


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Scalar Data Types

A scalar data type holds a single value and has no internal components. Scalar datatypes can be classified into four categories:

Number

Character

Date

Boolean

BASESCALAR DATA TYPES

CHAR [(maximum_length)] VARCHAR2(maximum_length)

LONG LONGRAW NUMBER [(precesion, scale)] BINARY_INTEGER

PLS_INTEGER

BOOLEAN


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Base Scalar Data Types

Data Type Description

CHAR [(maximum_length)] Base type for fixed-length character data up to 32,767 bytes. If you do not specify amaximum_length, the default length is set to 1.

VARCHAR2

(maximum_length)

Base type for variable-length character data up to 32, 767 bytes. There is no default size forVARCHAR2variables and constants.

LONG Base type for variable-length character data up to 32, 760 bytes. Use LONG data type to

store variable-length character strings. You can insert any LONG value into a LONGdatabase column because the maximum width ofLONG column is 2**31 bytes. However,you cannot retrieve a value longer than 32760 bytes for a LONG column into a LONG

variable.

LONGRAW Base type for binary data and byte strings up to 32, 760 bytes. LONGRAW is not interpreted

by PL/SQL

NUMBER [(precision,

scale)]

Number having precision p and scale s. The precision p can range from 1 to 38. The scale s

can range from -84 to 127.

BINARY_INTEGER Base type for integers between -2, 147, 483, 647 and 2,147, 483, 647.

PLS_INTEGER Base type for signed integers between -2,147, 483,647 and 2,147, 2483, 647. PLS_INTEGER

values require less storage and are faster than NUMBER and BINARY_INTEGER values.

BOOLEAN Base type that stores one of three possible values used for logical calculations: TRUE,FALSE, or NULL


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Data Type Description

DATE Base type for dates and time. DATE values include the time of day in seconds since midnight.

The range for date is between 4712 B.C. and 9999 A.D.

TIMESTAMP The TIMESTAMP data type, which extends the DATE data type, stores the year, month, day,hour, minute, and second. The syntax is : TIMESTAMP [(precession)]where the

optional parameter precision specifies the number of digits in the fractional of the secondsfield. You cannot use a symbolic constant or variable to specify the precision; you mustuse an integer literal in the range 0 .. 9. The default is 6.

TIMESTAMP WITHTIME

ZONE

The TIMESTAMP WITHTIME ZONE data type, which extends the TIMESTAMP data type,

includes a time-zone displacement. The time-zone displacement is the difference (in hoursand minutes) between local time and Coordinated Universal Time (UTC), formerly knownas Greanwich Mean Time. The syntax is: TIMESTAMP [(precision)]WITHTIMEZONE where the optional parameter precision specifies the number of digits in the

fractional part of the seconds field. You cannot use a symbolic constant or variable tospecify the precision; you must use an integer literal in the range 0 .. 9. The default is 6.

TIMESTAMP WITH LOCAL

TIME ZONE

The TIMESTAMP WITH LOCAL TIME ZONE data type, which extends TIMESTAMP data

type, includes a time-zone displacement. The time-zone displacement is the difference (in

hours and minutes) between local time and Coordinated Universal Time (UTC). Thesyntax is TIMESTAMP [(precision)]WITH LOCAL TIME ZONE where the optional

parameter precision specifies the number of digits in the fractional part of the secondsfield. You cannot use the symbolic constant or variable specify the precision; you must use

an integer or literal in the rang 0 .. 9. The default is 6.This data type differs from TIMESTAMP WITHTIME ZONE in that when you insert a value

into a database column, the value is normalized to the database time zone, and the time-zone displacement is not stored in the column. When you retrieve the value, Oraclereturns the value in you local session time zone.


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INTERVAL YEARTOMONTH You use the INTERVAL YEARTOMONTH data type to store and manipulate intervals of

years and months. The syntax is INTERVAL YEARTOMONTH [(precision)]TOMONTH where year_precision specifies the number of digits in the years field. You cannot

use a symbolic constant or variable to specify the precision; you must use an integer literal inthe range 0 .. 4. The default is 2..

INTERVAL DAYTO SECOND You use the INTERVAL DAYTO SECOND data type to store and manipulate intervals ofdays, hours, minutes, and seconds. The syntax is : INTERVAL DAY [(precision1)]TOSECOND [(precision2)]where precesion1 and precision2 specify the number of digits

in the days field and seconds field, respectively. In both cases, you cannot use a symbolicconstant or variable to specify the precision; you must use an integer literal in the range 0 .. 9.

The defaults are 2 and 6, respectively.


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The %TYPE Attribute

When declaring PL/SQL variables, the developer must ensure the variable is of the correctdata type and precision. If not, PL/SQL error will occur during execution.

Rather than hard coding the data type and precision of a variable, the developer can usethe %TYPE attribute to declare a variable according to another previously declared variableor database column.

The %TYPE attribute is most often used when the value stored in the variable will bederived from a table in the database.

Syntax:

identifier Table.column_name%TYPE

Examples:

...v_name employees.last_name%TYPE;v_salary NUMBER(7,2);

...


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Declaring Boolean Variables

Only the values TRUE, F

ALSE, and NULL can be assigned to a Boolean variable.

The variables are compared by the logical operators AND, OR, and NOT.

The variables always yield TRU, FALSE, or NULL.

Arithmetic, character, and date expression can be use to return a Boolean value.

Examples:

v_sal1 := 3000;v_sal2 := 4000;

The expression yields to TRUE.

v_sal1 < v_sal2.

Declare and initialize a Boolean variable

DECLARE

v_flag BOOLEAN := FALSE;BEGIN

v_flag := TRUE;END;


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LOB Data Type Variables

LOB (large object) data type, can store block of unstructured data (such as text, graphicimages, video clips, and sound wave forms) up to 4 gigabytes in size. LOB data typesallow efficient, random, piecewise access to the data and can be attributes of an objecttype. LOBs also support random access to data.

CLOB (character large object) data type is used to store large blocks of

single-byte character data in the database in line (inside the row) or out ofline (outside the row). (i.e. BOOK)

BLOB (binary large object) data type is use to store large binary objects inthe database in line (inside the row) or out of line (outside the row). (i.e.PHOTO)

BFILE (binary file) data type is used to store large binary objects inoperating system files outside the database. (i.e. MOVIE)

NCLOB (national language character large object) data type is used tostore large blocks of single-byte or fixed-width multibyte NCHAR unicodedata in the database, in line or out of line.


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BIND Variables

A bind variable is a variable that you can declare in a host environment. Bind variables canbe used to pass run-time values, either number or character, into or out of one or morePL/SQL programs.

Creating Bind Variables

To declare a bind variable in the iSQL*Plus environment, use the command VARIABLE.

For example:

Developer declare a variable type ofNUMBERorVARCHAR2 as follows:

VARIABLE return_code NUMBERVARIABLE return_msgVARCHAR2(3)


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Using Bind Variables

To reference a bind variable in PL/SQL, you must prefix its name with a colon (:).

Example:

VARIABLE g_salary NUMBER

BEGINSELECT salaryINTO :g_salaryFROM employees

WHERE employee_id = 180;END;/PRINT g_salary


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Referencing Non-PL/SQL Variables

To reference host variables, you must prefix the references with a colon (:) to distinguishthem from declared PL/SQL variables.

Example:

SET VERIFY OFF

VARIABLE g_monthly_sal NUMBERDEFINE p_annual_sal = 5000

DECLAREv_sal NUMBER(9,2) := &p_annual_sal;

BEGIN:g_monthly_sal := v_sal/12;

END;

/PRINT g_monthly_sal

Note: The DEFINE command specifies a user variable and assigns it a CHARvalue.


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DBMS_OUTPUT.PUT_LINE

You have seen that you can declare a host variable, reference it in a PL/SQL block, andthen display its contents in iSQL*Plus using the PRINT command.

Another option for displaying information from a PL/SQL block is DBMS_OUTPUT.PUTLINE.

An Oracle-supplied packaged procedure

An alternative for displaying data from a PL/SQL block

Must be enabled in iSQL*Plus with SET SERVEROUTPUT ON.


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DBMS_OUTPUT.PUT_LINE

Example:

SET SERVEROUTPUT ONDEFINE p_annual_sal = 60000DECLARE

v_sal NUMBER(9,2) := &pa_annual_sal;

BEGINv_sal := v_sal/12;DBMS_OUTPUT.PUT_LINE (Themonthlysalary is ||

TO_CHAR(v_sal));END;/

The output is:

The monthly salary is 5000PL/SQL procedure successfully completed.


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Questions?Questions?


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Practice ExercisePractice Exercise


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PLSQL Part1 Declaring Variables

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