DDL, or Data Definition Language, is used to define and manage the structure of database objects. This includes commands like `CREATE`, `ALTER`, and `DROP` to build, modify, and delete tables, schemas, and other database structures.

DML, or Data Manipulation Language, is used to manage the data within database objects. Commands like `INSERT`, `UPDATE`, `DELETE`, and `SELECT` are used to add, modify, remove, and retrieve data rows.

Can `SELECT` change data?

By default, no. `SELECT` statements are designed to retrieve data without altering it. While some database systems might have extensions or specific configurations that allow `SELECT` to trigger side effects, standard SQL treats `SELECT` as a read-only operation.

☁️ Cloud & Databases

SQL's Inner Workings: DDL vs. DML & Why It Matters

Forget dry syntax. This is about the muscle and mind behind your database queries, from structuring the vault to asking the sharpest questions.

Open Source Beat Apr 12, 2026 4 min read

Diagram showing the distinction between database structure (DDL) and data manipulation (DML) with arrows indicating command types.

⚡ Key Takeaways

Distinguishing between DDL (structure) and DML (data) is critical for database stability and operational sanity. 𝕏
The `WHERE` clause is the primary tool for filtering rows in `SELECT`, `UPDATE`, and `DELETE` operations, preventing unintended data modification. 𝕏
`CASE WHEN` allows for the creation of derived values and conditional logic directly within queries, enhancing data interpretation without schema changes. 𝕏

Written by

Ibrahim Samil Ceyisakar

Founder and Editor in Chief. Technology entrepreneur tracking AI, digital business, and global market trends.

#database #ddl #dml #querying #sql

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Originally reported by Dev.to

⚡ Key Takeaways

The 60-Second TL;DR

Ibrahim Samil Ceyisakar

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