DML (Data Manipulation Language):
- What is it: DML is a subset of SQL used to interact with and manipulate data stored in a database. It primarily includes commands for querying, inserting, updating, and deleting data in tables.
- What it’s used for: DML is used for retrieving and modifying data within a database. It allows users to perform operations such as reading data for reporting, adding new records, updating existing records, and deleting records.
- Examples: SELECT (retrieving data), INSERT (adding data), UPDATE (modifying data), DELETE (removing data).
DDL (Data Definition Language):
- What is it: DDL is a subset of SQL used for defining and managing the structure of a database. It includes commands for creating, modifying, and deleting database objects such as tables, indexes, and constraints.
- What it’s used for: DDL is used for defining the database schema, creating or altering tables, specifying constraints, and defining relationships between tables. It sets the structure that DML operates on.
- Examples: CREATE TABLE (creating tables), ALTER TABLE (modifying tables), DROP TABLE (deleting tables).
DCL (Data Control Language):
- What is it: DCL is a subset of SQL used for managing permissions, access control, and security within a database. It includes commands for granting and revoking privileges to users and roles.
- What it’s used for: DCL is used for controlling who can access and perform actions on database objects. It ensures the security and integrity of data by allowing or denying specific operations to users or roles.
- Examples: GRANT (giving privileges), REVOKE (revoking privileges).
SQL Commands
| DDL | DML | DCL |
|---|---|---|
| CREATE TABLE | SELECT | GRANT |
| ALTER TABLE | INSERT | REVOKE |
| DROP TABLE | UPDATE | COMMIT |
| DELETE |
How they relate to each other:
- DDL, DML, and DCL are all essential components of SQL that work together to manage and manipulate data within a database.
- DDL is used to define the structure and organization of data (e.g., tables, columns, constraints), creating the foundation for data storage.
- DML operates on the structure defined by DDL by retrieving, modifying, or deleting data stored in tables.
- DCL ensures that the right users or roles have appropriate permissions to perform DML and DDL operations, protecting the data’s security and integrity.
In summary, DDL sets up the database structure, DML interacts with the data within that structure, and DCL controls who has access and what actions they can perform on the data and schema. These three components work in tandem to manage and secure a database.