PL/SQL Block Structure

Every piece of PL/SQL code is organised into a block — a self-contained unit with a defined structure. Understanding the block is the foundation of everything else in PL/SQL.

The Four Sections

DECLARE
  -- Optional: variable declarations, cursor declarations, type definitions
BEGIN
  -- Mandatory: executable statements (SQL + procedural logic)
EXCEPTION
  -- Optional: error handlers
END;
/

Section	Required?	Purpose
DECLARE	No	Declare local variables, cursors, and types
BEGIN	Yes	The code that actually runs
EXCEPTION	No	Handle runtime errors gracefully
END	Yes	Closes the block

Your First PL/SQL Block

BEGIN
  DBMS_OUTPUT.PUT_LINE('Hello, PL/SQL!');
END;
/

DBMS_OUTPUT.PUT_LINE writes a line of text to the output buffer. In SQL Developer, enable output with View → DBMS Output. In SQL*Plus, run SET SERVEROUTPUT ON first.

Block with Declarations

DECLARE
  v_message VARCHAR2(100) := 'Hello, World!';
  v_count   NUMBER        := 0;
BEGIN
  v_count := v_count + 1;
  DBMS_OUTPUT.PUT_LINE(v_message);
  DBMS_OUTPUT.PUT_LINE('Count: ' || v_count);
END;
/

Nested Blocks

Blocks can be nested inside other blocks. The inner block can access variables from the outer block, but not vice versa:

DECLARE
  v_outer VARCHAR2(20) := 'outer';
BEGIN
  DECLARE
    v_inner VARCHAR2(20) := 'inner';
  BEGIN
    DBMS_OUTPUT.PUT_LINE(v_outer || ' and ' || v_inner);
  END;
  -- v_inner is not accessible here
  DBMS_OUTPUT.PUT_LINE(v_outer);
END;
/

Anonymous vs Named Blocks

An anonymous block has no name — you type it and run it directly. It cannot be called by other code.

A named block (procedure, function, package) is stored in the database and can be called by name. You'll cover those in later lessons.

Comments

-- Single-line comment

/*
  Multi-line
  comment
*/

The String Concatenation Operator

PL/SQL uses || (double pipe) to concatenate strings:

DBMS_OUTPUT.PUT_LINE('Value is: ' || v_count);

Common Mistakes

• Forgetting the semicolon ; after each statement
• Missing the / at the end to run the block
• Forgetting SET SERVEROUTPUT ON in SQL*Plus (output won't appear)
• Declaring variables in the BEGIN section instead of DECLARE