PL/SQL vs. SQL – Understanding the Difference

Structured Query Language (SQL) gives us complete access to our data. But it’s important to note: while SQL is powerful, it lacks the core programming constructs found in typical programming languages.

Limitations of SQL:

SQL, by itself, cannot:

Loop through records and process each individually.
Store code securely on the server (everything executes on the client side).
Handle exceptions or unexpected behaviors.
Work with advanced data types like:
- Variables
- Parameters
- Collections
- Records & Arrays
- Objects & Cursors
- BFILEs (binary file references)

In short: SQL = Data Access, not programming logic.

Enter PL/SQL

PL/SQL (Procedural Language SQL) enhances SQL by adding all the programming capabilities SQL lacks. It is Oracle’s proprietary extension of SQL that allows:
✅ Loops
✅ Variables
✅ Exception Handling
✅ Stored Procedures & Functions
✅ Stronger Code Security (stored on server)
✅ Better Performance (procedural blocks reduce round-trips)

PL/SQL Practical Example: Looping Over BOOKS and AUTHORS

Here’s how the earlier SQL query becomes a PL/SQL block that:

Loops through records
Checks author’s last name
Outputs conditional text

Examples:

SET SERVEROUTPUT ON

DECLARE
  v_title       books.title%TYPE;
  v_first_name  authors.first_name%TYPE;
  v_last_name   authors.last_name%TYPE;

  CURSOR book_cur IS
    SELECT b.title, a.first_name, a.last_name
    FROM authors a, books b
    WHERE a.id = b.author1;

BEGIN
  DBMS_OUTPUT.ENABLE(1000000);
  OPEN book_cur;
  
  LOOP
    FETCH book_cur INTO v_title, v_first_name, v_last_name;
    EXIT WHEN book_cur%NOTFOUND;

    IF v_last_name = 'Hardman' THEN
      DBMS_OUTPUT.PUT_LINE('Ron Hardman co-authored ' || v_title);
    ELSE
      DBMS_OUTPUT.PUT_LINE('Ron Hardman did not write ' || v_title);
    END IF;
    
  END LOOP;
  
  CLOSE book_cur;

EXCEPTION
  WHEN OTHERS THEN
    DBMS_OUTPUT.PUT_LINE(SQLERRM);
END;
/

Difference Between SQL and PL/SQL

Feature / Basis	SQL (Structured Query Language)	PL/SQL (Procedural Language/SQL)
Type	Data-oriented query language	Procedural programming language with SQL integration
Usage	Used to perform single operations like SELECT, INSERT, etc.	Used to perform multiple operations with logic
Execution	Executes one statement at a time	Executes a block of code/statements at once
Control Structures	❌ Not available	✅ Supports IF, LOOP, WHILE, CASE, etc.
Exception Handling	❌ Not supported	✅ Robust exception handling available
Variables & Data Types	❌ Cannot declare variables	✅ Variables, records, cursors, and data types supported
Code Storage	Client-side only	Can be stored and executed from server
Procedures & Functions	❌ Not possible	✅ Can create stored procedures, functions, packages
Performance Optimization	Requires multiple round-trips to DB	Reduces network traffic via block execution
Support in Oracle	ANSI Standard + Oracle-specific extensions	Oracle proprietary language
Purpose	Interact directly with the database	Add logic and structure around SQL

What is SQL?

SQL is a declarative language. You tell it what you want (like fetching data), and it figures out how to do it. It’s used for:

Querying data (SELECT)
Modifying data (INSERT, UPDATE, DELETE)
Managing schema objects (CREATE, DROP, ALTER)

❗ But SQL cannot handle logic, looping, or advanced operations by itself.

What is PL/SQL?

PL/SQL is Oracle’s extension of SQL. It combines procedural logic with SQL capabilities, allowing:

Loops
Conditional statements
Variables
Error handling
Creating and storing procedures, functions, and triggers

Best suited for business logic, batch processing, automation, and reusable code.