Getting Started with SQL DDL for Database Structure

Databases are more than rows of data—they’re carefully structured systems. SQL DDL (Data Definition Language) is used to build and modify this structure. It’s the part of SQL that deals with how data is stored, not the data itself.

What Is SQL DDL?

DDL is used to manage database objects like tables, indexes, and views. It doesn’t interact with the actual records but focuses on the schema that holds them.

Key commands:

• CREATE: Start a new table or object

• ALTER: Adjust a table’s design

• DROP: Remove an object

• TRUNCATE: Clear data while keeping the table

Examples of DDL in Practice

Here are examples of how DDL works in real SQL:

Create a new table

CREATE TABLE employees (
  id INT,
  name VARCHAR(100)
);

Add a column

ALTER TABLE employees ADD salary DECIMAL(10, 2);

Remove the table

DROP TABLE employees;

Clear table contents

TRUNCATE TABLE employees;

These commands are essential when setting up or maintaining your schema.

FAQ

What does SQL DDL stand for?

Data Definition Language—it handles schema and structure.

Is it different from DML?

Yes, DML changes data. DDL changes structure.

Can I undo a DDL change?

Only in systems with transactional DDL or if you’ve backed up your schema.

How do I see the table structure?

Use SHOW CREATE TABLE or a tool like DbVisualizer to inspect object definitions.

Conclusion

Using SQL DDL effectively helps you manage structure cleanly as your application scales. Knowing these basics is key to more control over your schema and better teamwork around database changes. Read SQL DDL: The Definitive Guide on Data Definition Language for a full walkthrough and examples.