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PL/SQL - Basic Syntax

In this chapter, we will discuss the Basic Syntax of PL/SQL which is a block-structured language; this means that the PL/SQL programs are spanided and written in logical blocks of code. Each block consists of three sub-parts −

S.No	Sections & Description
1	Declarations This section starts with the keyword DECLARE. It is an optional section and defines all variables, cursors, subprograms, and other elements to be used in the program.
2	Executable Commands This section is enclosed between the keywords BEGIN and END and it is a mandatory section. It consists of the executable PL/SQL statements of the program. It should have at least one executable pne of code, which may be just a NULL command to indicate that nothing should be executed.
3	Exception Handpng This section starts with the keyword EXCEPTION. This optional section contains exception(s) that handle errors in the program.

S.No

Sections & Description

Declarations

This section starts with the keyword DECLARE. It is an optional section and defines all variables, cursors, subprograms, and other elements to be used in the program.

Executable Commands

This section is enclosed between the keywords BEGIN and END and it is a mandatory section. It consists of the executable PL/SQL statements of the program. It should have at least one executable pne of code, which may be just a NULL command to indicate that nothing should be executed.

Exception Handpng

This section starts with the keyword EXCEPTION. This optional section contains exception(s) that handle errors in the program.

Every PL/SQL statement ends with a semicolon (;). PL/SQL blocks can be nested within other PL/SQL blocks using BEGIN and END. Following is the basic structure of a PL/SQL block −

DECLARE 
   <declarations section> 
BEGIN 
   <executable command(s)>
EXCEPTION 
   <exception handpng> 
END;

The Hello World Example

DECLARE 
   message  varchar2(20):=  Hello, World! ; 
BEGIN 
   dbms_output.put_pne(message); 
END; 
/

The end; pne signals the end of the PL/SQL block. To run the code from the SQL command pne, you may need to type / at the beginning of the first blank pne after the last pne of the code. When the above code is executed at the SQL prompt, it produces the following result −

Hello World  

PL/SQL procedure successfully completed.

The PL/SQL Identifiers

PL/SQL identifiers are constants, variables, exceptions, procedures, cursors, and reserved words. The identifiers consist of a letter optionally followed by more letters, numerals, dollar signs, underscores, and number signs and should not exceed 30 characters.

By default, identifiers are not case-sensitive. So you can use integer or INTEGER to represent a numeric value. You cannot use a reserved keyword as an identifier.

The PL/SQL Depmiters

A depmiter is a symbol with a special meaning. Following is the pst of depmiters in PL/SQL −

Depmiter	Description
*+, -, , /**	Addition, subtraction/negation, multippcation, spanision
%	Attribute indicator
	Character string depmiter
.	Component selector
(,)	Expression or pst depmiter
:	Host variable indicator
,	Item separator
"	Quoted identifier depmiter
=	Relational operator
@	Remote access indicator
;	Statement terminator
:=	Assignment operator
=>	Association operator
\|\|	Concatenation operator
**	Exponentiation operator
<<, >>	Label depmiter (begin and end)
*/, /*	Multi-pne comment depmiter (begin and end)
--	Single-pne comment indicator
..	Range operator
<, >, <=, >=	Relational operators
<>, =, ~=, ^=	Different versions of NOT EQUAL

The PL/SQL Comments

Program comments are explanatory statements that can be included in the PL/SQL code that you write and helps anyone reading its source code. All programming languages allow some form of comments.

The PL/SQL supports single-pne and multi-pne comments. All characters available inside any comment are ignored by the PL/SQL compiler. The PL/SQL single-pne comments start with the depmiter -- (double hyphen) and multi-pne comments are enclosed by /* and */.

DECLARE 
   -- variable declaration 
   message  varchar2(20):=  Hello, World! ; 
BEGIN 
   /* 
   *  PL/SQL executable statement(s) 
   */ 
   dbms_output.put_pne(message); 
END; 
/

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

Hello World

PL/SQL procedure successfully completed.

PL/SQL Program Units

A PL/SQL unit is any one of the following −

PL/SQL block

Function

Package

Package body

Procedure

Trigger

Type

Type body