SQL Commands: DDL, DML, DQL

Explore Data Definition Language for schema modifications, Data Manipulation Language for data handling, and Data Query Language for effective retrieval

40 Participants 30 Minutes Beginner

Structured Query Language (SQL) serves as the backbone of database management systems, enabling efficient communication with databases. In this comprehensive guide, we delve into the three key categories of SQL commands: Data Definition Language (DDL), Data Manipulation Language (DML), and Data Query Language (DQL). Together, they form the essential toolkit for interacting with databases, facilitating schema modifications, data handling, and effective data retrieval.



Data Definition Language (DDL): Shaping the Foundation

DDL commands focus on the structure of the database, allowing users to define and modify the schema. These commands play a pivotal role in database design and management. Common DDL commands include:

1. CREATE TABLE: The foundation of any database begins with the creation of tables. This command defines the structure, specifying column names, data types, and constraints.

2. ALTER TABLE: As data requirements evolve, so does the database structure. The ALTER TABLE command facilitates modifications, such as adding or dropping columns, and altering data types.

3. DROP TABLE: When a table is no longer needed, the DROP TABLE command removes it from the database, freeing up resources.

4. CREATE INDEX: Indexing enhances query performance by providing quick access to specific rows based on indexed columns.

DDL commands empower database administrators to shape the architecture of the database, ensuring it aligns with the evolving needs of the organization.


Data Manipulation Language (DML): Crafting and Controlling Data

DML commands revolve around the manipulation and handling of data within the database. They enable users to insert, update, and delete records. Key DML commands include:

1. SELECT: While often associated with DQL, SELECT also plays a crucial role in DML. It retrieves data from one or more tables, offering a versatile tool for data analysis.

2. INSERT: Adding new records to a table is accomplished with the INSERT command. It allows users to specify values for each column or retrieve values from another table.

3. UPDATE: When existing records require modification, the UPDATE command comes into play. It enables users to change the values of specific columns in one or more records.

4. DELETE: The DELETE command removes records from a table based on specified conditions, maintaining data integrity.

DML commands empower users to interact with the data, ensuring it remains accurate, up-to-date, and aligned with business requirements.


Data Query Language (DQL): Unveiling the Power of Retrieval

DQL commands focus on retrieving data from the database, allowing users to pose complex queries and obtain meaningful insights. The cornerstone of DQL is the SELECT statement, which enables:

1. Filtering: SELECT statements can include WHERE clauses to filter data based on specified conditions, refining the result set.

2. Joining: Multiple tables can be joined together, providing a holistic view of the data distributed across different entities.

3. Grouping and Aggregation: DQL allows for grouping data based on specific columns and performing aggregate functions like SUM, AVG, COUNT, etc.

By mastering DQL, users unlock the ability to extract valuable information from databases, supporting informed decision-making processes.



In summary, SQL commands, encompassing DDL, DML, and DQL, form the backbone of efficient database management. DDL shapes the foundation, DML crafts and controls data, and DQL unveils the power of retrieval. With a comprehensive understanding of these commands, users can navigate the intricate landscape of database operations, ensuring data integrity, efficiency, and meaningful insights.



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