Data Definition Language (DDL) is a subset of Structured Query Language (SQL) used to define and manage database structures. DDL primarily focuses on creating, modifying, and deleting database schema objects such as tables, indexes, views, and constraints. Unlike Data Manipulation Language (DML), which deals with data handling, DDL operations affect the database schema itself and are typically auto-committed, meaning changes are permanent.
Key Characteristics of Data Definition Language (DDL)
- Schema Definition – DDL commands define the structure of a database.
- Auto-Commit Transactions – Changes made using DDL commands are permanent and cannot be rolled back.
- No Data Manipulation – Unlike DML, DDL does not handle inserting, updating, or deleting records.
- Security and Access Control – DDL commands define user permissions and roles.
How are DDL Statements Used in Database?
DDL statements play a crucial role in structuring and organizing data within relational databases. These statements help database administrators and developers define the architecture of a database before inserting or manipulating data.
DDL is used to:
- Constraints – Constraints are predefined rules applied to data columns within a table to maintain data integrity and consistency. They define restrictions on the type of data that can be stored and ensure that entries adhere to specified conditions. By enforcing these constraints, databases enhance accuracy, reliability, and overall data quality.
- DDL Commands – These commands are used to define and manage database structures, including operations such as CREATE, ALTER, DROP, TRUNCATE, COMMENT, and RENAME. They enable the creation, modification, and removal of database objects, ensuring efficient organization and management of data.
- Modifying Tables – DDL commands allow modifications to the structure of existing tables, enabling users to add or remove columns, alter data types within a column, and rename columns as needed. These operations ensure that the database schema remains adaptable to evolving business requirements.
Common DDL Commands and Their Functions
CREATE
The CREATE command is used to define a new database object, such as tables, indexes, and views.
Example – Creating a table named ‘Employees’,
