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SQL & Databases Masterclass Course

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LESSON WORKSPACEIntermediate

SQL Lesson 15: Deleting rows

Introduction & Core Concept

To permanently remove obsolete, cancelled, or incorrect records from a database table, we execute the DELETE FROM command.

DELETE FROM table_name WHERE condition;
CRITICAL WARNING: Exactly like UPDATE, omitting the WHERE constraint on a DELETE FROM query will instantly wipe out EVERY SINGLE ROW in your table, leaving you with a completely empty schema!
Why & Where We Use It
  • Why We Use It: Purges old data, removes test accounts, and ensures compliance with privacy regulations like GDPR (the right to be forgotten).
  • Where We Use It: Clearing out cancelled shopping carts, deleting expired authentication tokens, and removing spam accounts.
    • Real-World Example

    ShopMart wants to clean up their transaction tables by purging all orders that were permanently marked as 'Cancelled'. They execute a DELETE FROM query targeting WHERE status = 'Cancelled'.

    Best Practices: What to Do & What NOT to Do
  • What to Do: Consider using Soft Deletions instead of physical DELETE queries for critical business tables. A soft delete involves adding an is_deleted boolean column and running an UPDATE to set it to true, allowing you to restore data easily if needed.
  • What NOT to Do: Never execute a DELETE query on tables with active Foreign Key constraints without verifying whether cascading deletions are enabled, as you could accidentally delete related child rows across the database!
    • Syntax & Pro Tips
    DELETE FROM orders WHERE status = 'Cancelled';
    Interactive Sandboxed Terminal (Preloaded DB Schema: SHOPMART)
    SQL Query WorkspaceSQLite v3.45 (WASM Mode)
    QUICK INSERT:
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