Oracle DISTINCT Clause 💎

Mentor's Note: Your database might have 1,000 employees, but maybe they only live in 5 different cities. DISTINCT helps you see those unique values without the repetition. 💡

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🌟 The Scenario: The City Census 📍

• Goal: Find out which cities our company operates in.
• Problem: If 100 people live in Surat, you don't want to see "Surat" 100 times.
• Action: You use DISTINCT to get a clean, unique list.

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💻 1. Syntax & Examples

SELECT DISTINCT column_name FROM table_name;

Example: Unique Job Titles

SELECT DISTINCT job_id FROM employees;

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🏗️ Architect's Note: The Unique Sort 🛡️

When you run DISTINCT, Oracle internally performs a SORT UNIQUE or HASH UNIQUE operation. This means the database has to scan and compare every row to find duplicates.

• Pro Tip: If you know a table only has unique values (like a Primary Key column), using DISTINCT is a waste of CPU power!

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📈 Learning Path

• ← Back: ORDER BY
• Next: WHERE →