Difference Between DDL and DML
Introduction: When it comes to managing databases, two fundamental concepts are Data Definition Language (DDL) and Data Manipulation Language (DML). Understanding their differences and purposes is crucial for anyone working with databases. In this article, we will explore DDL and DML in detail, provide examples, highlight their uses, and present a comprehensive table of differences between the two.
What is DDL?
Data Definition Language (DDL) is a set of SQL commands used to define and manage the structure of the database. DDL statements allow you to create, modify, and delete database objects such as tables, views, indexes, and more.
Examples of DDL:
- CREATE TABLE: Creates a new table in the database.
- ALTER TABLE: Modifies the structure of an existing table.
- CREATE INDEX: Creates an index on a table.
- DROP TABLE: Deletes an existing table from the database.
Uses of DDL:
DDL is primarily used by database administrators and developers to define the schema of a database and manage its structure. It allows them to create, modify, and delete database objects based on application requirements or system changes.
What is DML?
Data Manipulation Language (DML) is a subset of SQL used to manage data within the database. DML statements are responsible for querying, inserting, updating, and deleting data records stored in the tables.
Examples of DML:
- SELECT: Retrieves data from one or more tables.
- INSERT: Adds new records to a table.
- UPDATE: Modifies existing records in a table.
- DELETE: Removes records from a table.
Uses of DML:
DML is often used by developers and end-users to interact with the database. It allows them to retrieve, insert, update, and delete data records based on specific criteria, performing tasks such as searching, modifying, or removing data.
Differences between DDL and DML:
| Difference Area | DDL | DML |
|---|---|---|
| Function | Used for defining and managing the structure of the database. | Used for querying, inserting, updating, and deleting data records within tables. |
| Usage | Database administrators and developers use DDL. | Developers and end-users use DML. |
| Operations | Creates, modifies, and deletes database objects. | Retrieves, inserts, updates, and deletes data records. |
| Examples | CREATE TABLE, ALTER TABLE, DROP TABLE, CREATE INDEX | SELECT, INSERT, UPDATE, DELETE |
| Focus | Structure definition and management. | Data retrieval and manipulation. |
| Impact | Changes affect the structure of the database. | Changes affect the data stored in the database. |
| Dependency | DML statements depend on the existence of DDL-defined database objects. | DDL statements are independent and do not directly rely on DML. |
| Execution Order | DDL statements are executed before DML. | DML statements are executed after DDL. |
| Data Integrity | DDL enforces structural constraints such as primary keys and foreign keys. | DML ensures data integrity by performing operations based on defined constraints. |
| System Privileges | DDL requires higher-level privileges to create or modify database objects. | DML requires lower-level privileges to manipulate data within the tables. |
Conclusion:
In summary, DDL and DML serve different purposes in database management. DDL focuses on defining and managing the structure of the database, while DML deals with retrieving, inserting, updating, and deleting data records. Understanding the distinctions between DDL and DML is essential for effective database management and development.
People Also Ask:
Q: What happens if DML is executed before DDL?
If DML is executed before DDL, it will result in errors because the database objects needed for DML operations would not exist.
Q: Can DDL statements be rolled back?
Most DDL statements in SQL cannot be rolled back once executed. However, some DBMS provides a rollback feature for certain DDL operations.
Q: What privileges are required for executing DDL statements?
DDL statements require higher-level privileges, such as those granted to database administrators or users with appropriate system privileges.
Q: Is it possible to use DDL and DML in the same transaction?
Yes, it is possible to use DDL and DML in the same transaction. However, DDL statements typically commit the transaction, so any pending DML statements will be automatically committed as well.
Q: How does DML help ensure data integrity?
DML enforces data integrity by performing operations based on defined constraints such as primary key, foreign key, and unique key constraints. These constraints prevent invalid data from being inserted or maintained in the tables.
