PL/SQL - Basic Syntax

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PL/SQL is a block-structured language, meaning that PL/SQL programs are divided and written in logical blocks of code. Each block consists of three sub-parts:

S.N.Sections & Description
1Declarations
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.
2Executable 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 line of code, which may be just a NULL command to indicate that nothing should be executed.
3Exception Handling
This section starts with the keyword EXCEPTION. This section is again optional and 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. Here is the basic structure of a PL/SQL block:

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

The 'Hello World' Example:

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

The end; line signals the end of the PL/SQL block. To run the code from SQL command line, you may need to type / at the beginning of the first blank line after the last line of the code. When the above code is executed at 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 Delimiters

A delimiter is a symbol with a special meaning. Following is the list of delimiters in PL/SQL:

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

The PL/SQL Comments

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

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

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

When the above code is executed at 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

Each of these units will be discussed in the forthcoming chapters.



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