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PL/SQL – Variables

In this chapter, we will discuss Variables in Pl/SQL. A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in PL/SQL has a specific data type, which determines the size and the layout of the variable”s memory; the range of values that can be stored within that memory and the set of operations that can be applied to the variable.

The name of a PL/SQL variable consists of a letter optionally followed by more letters, numerals, dollar signs, underscores, and number signs and should not exceed 30 characters. By default, variable names are not case-sensitive. You cannot use a reserved PL/SQL keyword as a variable name.

PL/SQL programming language allows to define various types of variables, such as date time data types, records, collections, etc. which we will cover in subsequent chapters. For this chapter, let us study only basic variable types.

Variable Declaration in PL/SQL

PL/SQL variables must be declared in the declaration section or in a package as a global variable. When you declare a variable, PL/SQL allocates memory for the variable”s value and the storage location is identified by the variable name.

The syntax for declaring a variable is −

variable_name [CONSTANT] datatype [NOT NULL] [:= | DEFAULT initial_value]

Where, variable_name is a valid identifier in PL/SQL, datatype must be a valid PL/SQL data type or any user defined data type which we already have discussed in the last chapter. Some valid variable declarations along with their definition are shown below −

sales number(10, 2);
pi CONSTANT double precision := 3.1415;
name varchar2(25);
address varchar2(100);

When you provide a size, scale or precision limit with the data type, it is called a constrained declaration. Constrained declarations require less memory than unconstrained declarations. For example −

sales number(10, 2);
name varchar2(25);
address varchar2(100);

Initializing Variables in PL/SQL

Whenever you declare a variable, PL/SQL assigns it a default value of NULL. If you want to initialize a variable with a value other than the NULL value, you can do so during the declaration, using either of the following −

The DEFAULT keyword
The assignment operator

For example −

counter binary_integer := 0;
greetings varchar2(20) DEFAULT ''Have a Good Day

You can also specify that a variable should not have a NULL value using the NOT NULL constraint. If you use the NOT NULL constraint, you must explicitly assign an initial value for that variable.

It is a good programming practice to initialize variables properly otherwise, sometimes programs would produce unexpected results. Try the following example which makes use of various types of variables −

DECLARE
   a integer := 10;
   b integer := 20;
   c integer;
   f real;
BEGIN
   c := a + b;
   dbms_output.put_line(''Value of c: '' || c);
   f := 70.0/3.0;
   dbms_output.put_line(''Value of f: '' || f);
END;
/

When the above code is executed, it produces the following result −

Value of c: 30
Value of f: 23.333333333333333333

PL/SQL procedure successfully completed.

Variable Scope in PL/SQL

PL/SQL allows the nesting of blocks, i.e., each program block may contain another inner block. If a variable is declared within an inner block, it is not accessible to the outer block. However, if a variable is declared and accessible to an outer block, it is also accessible to all nested inner blocks. There are two types of variable scope −

Local variables − Variables declared in an inner block and not accessible to outer blocks.
Global variables − Variables declared in the outermost block or a package.

Following example shows the usage of Local and Global variables in its simple form −

DECLARE
   -- Global variables
   num1 number := 95;
   num2 number := 85;
BEGIN
   dbms_output.put_line(''Outer Variable num1: '' || num1);
   dbms_output.put_line(''Outer Variable num2: '' || num2);
   DECLARE
      -- Local variables
      num1 number := 195;
      num2 number := 185;
   BEGIN
      dbms_output.put_line(''Inner Variable num1: '' || num1);
      dbms_output.put_line(''Inner Variable num2: '' || num2);
   END;
END;
/

When the above code is executed, it produces the following result −

Outer Variable num1: 95
Outer Variable num2: 85
Inner Variable num1: 195
Inner Variable num2: 185

PL/SQL procedure successfully completed.

Assigning SQL Query Results to PL/SQL Variables

You can use the SELECT INTO statement of SQL to assign values to PL/SQL variables. For each item in the SELECT list, there must be a corresponding, type-compatible variable in the INTO list. The following example illustrates the concept. Let us create a table named CUSTOMERS −

(For SQL statements, please refer to the )

CREATE TABLE CUSTOMERS(
   ID   INT NOT NULL,
   NAME VARCHAR (20) NOT NULL,
   AGE INT NOT NULL,
   ADDRESS CHAR (25),
   SALARY   DECIMAL (18, 2),
   PRIMARY KEY (ID)
);

Table Created

Let us now insert some values in the table −

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (1, ''Ramesh'', 32, ''Ahmedabad'', 2000.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (2, ''Khilan'', 25, ''Delhi'', 1500.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (3, ''kaushik'', 23, ''Kota'', 2000.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (4, ''Chaitali'', 25, ''Mumbai'', 6500.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (5, ''Hardik'', 27, ''Bhopal'', 8500.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (6, ''Komal'', 22, ''MP'', 4500.00 );

The following program assigns values from the above table to PL/SQL variables using the SELECT INTO clause of SQL −

DECLARE
   c_id customers.id%type := 1;
   c_name  customers.name%type;
   c_addr customers.address%type;
   c_sal  customers.salary%type;
BEGIN
   SELECT name, address, salary INTO c_name, c_addr, c_sal
   FROM customers
   WHERE id = c_id;
   dbms_output.put_line
   (''Customer '' ||c_name || '' from '' || c_addr || '' earns '' || c_sal);
END;
/

When the above code is executed, it produces the following result −

Customer Ramesh from Ahmedabad earns 2000

PL/SQL procedure completed successfully

Khóa học lập trình tại Toidayhoc vừa học vừa làm dự án vừa nhận lương: Khóa học lập trình nhận lương tại trung tâm Toidayhoc

August 17, 2024

S.No	Category & Description
1	Scalar Single values with no internal components, such as a NUMBER, DATE, or BOOLEAN.
2	Large Object (LOB) Pointers to large objects that are stored separately from other data items, such as text, graphic images, video clips, and sound waveforms.
3	Composite Data items that have internal components that can be accessed individually. For example, collections and records.
4	Reference Pointers to other data items.

S.No	Date Type & Description
1	Numeric Numeric values on which arithmetic operations are performed.
2	Character Alphanumeric values that represent single characters or strings of characters.
3	Boolean Logical values on which logical operations are performed.
4	Datetime Dates and times.

S.No	Data Type & Description
1	PLS_INTEGER Signed integer in range -2,147,483,648 through 2,147,483,647, represented in 32 bits
2	BINARY_INTEGER Signed integer in range -2,147,483,648 through 2,147,483,647, represented in 32 bits
3	BINARY_FLOAT Single-precision IEEE 754-format floating-point number
4	BINARY_DOUBLE Double-precision IEEE 754-format floating-point number
5	NUMBER(prec, scale) Fixed-point or floating-point number with absolute value in range 1E-130 to (but not including) 1.0E126. A NUMBER variable can also represent 0
6	DEC(prec, scale) ANSI specific fixed-point type with maximum precision of 38 decimal digits
7	DECIMAL(prec, scale) IBM specific fixed-point type with maximum precision of 38 decimal digits
8	NUMERIC(pre, secale) Floating type with maximum precision of 38 decimal digits
9	DOUBLE PRECISION ANSI specific floating-point type with maximum precision of 126 binary digits (approximately 38 decimal digits)
10	FLOAT ANSI and IBM specific floating-point type with maximum precision of 126 binary digits (approximately 38 decimal digits)
11	INT ANSI specific integer type with maximum precision of 38 decimal digits
12	INTEGER ANSI and IBM specific integer type with maximum precision of 38 decimal digits
13	SMALLINT ANSI and IBM specific integer type with maximum precision of 38 decimal digits
14	REAL Floating-point type with maximum precision of 63 binary digits (approximately 18 decimal digits)

S.No	Data Type & Description
1	CHAR Fixed-length character string with maximum size of 32,767 bytes
2	VARCHAR2 Variable-length character string with maximum size of 32,767 bytes
3	RAW Variable-length binary or byte string with maximum size of 32,767 bytes, not interpreted by PL/SQL
4	NCHAR Fixed-length national character string with maximum size of 32,767 bytes
5	NVARCHAR2 Variable-length national character string with maximum size of 32,767 bytes
6	LONG Variable-length character string with maximum size of 32,760 bytes
7	LONG RAW Variable-length binary or byte string with maximum size of 32,760 bytes, not interpreted by PL/SQL
8	ROWID Physical row identifier, the address of a row in an ordinary table
9	UROWID Universal row identifier (physical, logical, or foreign row identifier)

Field Name	Valid Datetime Values	Valid Interval Values
YEAR	-4712 to 9999 (excluding year 0)	Any nonzero integer
MONTH	01 to 12	0 to 11
DAY	01 to 31 (limited by the values of MONTH and YEAR, according to the rules of the calendar for the locale)	Any nonzero integer
HOUR	00 to 23	0 to 23
MINUTE	00 to 59	0 to 59
SECOND	00 to 59.9(n), where 9(n) is the precision of time fractional seconds	0 to 59.9(n), where 9(n) is the precision of interval fractional seconds
TIMEZONE_HOUR	-12 to 14 (range accommodates daylight savings time changes)	Not applicable
TIMEZONE_MINUTE	00 to 59	Not applicable
TIMEZONE_REGION	Found in the dynamic performance view V$TIMEZONE_NAMES	Not applicable
TIMEZONE_ABBR	Found in the dynamic performance view V$TIMEZONE_NAMES	Not applicable

Data Type	Description	Size
BFILE	Used to store large binary objects in operating system files outside the database.	System-dependent. Cannot exceed 4 gigabytes (GB).
BLOB	Used to store large binary objects in the database.	8 to 128 terabytes (TB)
CLOB	Used to store large blocks of character data in the database.	8 to 128 TB
NCLOB	Used to store large blocks of NCHAR data in the database.	8 to 128 TB

S.No	Loop Type & Description
1	In this loop structure, sequence of statements is enclosed between the LOOP and the END LOOP statements. At each iteration, the sequence of statements is executed and then control resumes at the top of the loop.
2	Repeats a statement or group of statements while a given condition is true. It tests the condition before executing the loop body.
3	Execute a sequence of statements multiple times and abbreviates the code that manages the loop variable.
4	You can use one or more loop inside any another basic loop, while, or for loop.

S.No	Control Statement & Description
1	The Exit statement completes the loop and control passes to the statement immediately after the END LOOP.
2	Causes the loop to skip the remainder of its body and immediately retest its condition prior to reiterating.
3	Transfers control to the labeled statement. Though it is not advised to use the GOTO statement in your program.

S.No	Statement & Description
1	The IF statement associates a condition with a sequence of statements enclosed by the keywords THEN and END IF. If the condition is true, the statements get executed and if the condition is false or NULL then the IF statement does nothing.
2	IF statement adds the keyword ELSE followed by an alternative sequence of statement. If the condition is false or NULL, then only the alternative sequence of statements get executed. It ensures that either of the sequence of statements is executed.
3	It allows you to choose between several alternatives.
4	Like the IF statement, the CASE statement selects one sequence of statements to execute. However, to select the sequence, the CASE statement uses a selector rather than multiple Boolean expressions. A selector is an expression whose value is used to select one of several alternatives.
5	The searched CASE statement has no selector, and it”s WHEN clauses contain search conditions that yield Boolean values.
6	You can use one IF-THEN or IF-THEN-ELSIF statement inside another IF-THEN or IF-THEN-ELSIF statement(s).

Category: plsql

PL/SQL – Variables

Variable Declaration in PL/SQL

Initializing Variables in PL/SQL

Variable Scope in PL/SQL

Assigning SQL Query Results to PL/SQL Variables

PL/SQL Tutorial

PL/SQL Tutorial

Purpose of PL/SQL

Features of PL/SQL

Why to learn PL/SQL?

PL/SQL Block Structured

Applications of PL/SQL

Who Should Learn PL/SQL?

Prerequisites to learn PL/SQL

PL/SQL Jobs and Opportunities

Frequently Asked Questions about PL/SQL

PL/SQL – Data Types

PL/SQL Scalar Data Types and Subtypes

PL/SQL Numeric Data Types and Subtypes

PL/SQL Character Data Types and Subtypes

PL/SQL Boolean Data Types

PL/SQL Datetime and Interval Types

PL/SQL Large Object (LOB) Data Types

PL/SQL User-Defined Subtypes

NULLs in PL/SQL

PL/SQL – Loops

Labeling a PL/SQL Loop

The Loop Control Statements

PL/SQL – Conditions

PL/SQL – Environment Setup

Step 1

Step 2

Step 3

Step 4

Step 5

Step 6

Step 7

Step 8

Step 9

Step 10

Step 11

Final Step

Text Editor

PL/SQL – Constants and Literals

Declaring a Constant

The PL/SQL Literals

PL/SQL – Operators

Arithmetic Operators

Relational Operators

Comparison Operators

Logical Operators

PL/SQL Operator Precedence