SQL UPDATE Statement ✏️

Mentor's Note: People change. Prices change. Phone numbers change. The UPDATE statement is how your database keeps up with the real world. But be careful: forgetting a WHERE clause is the fastest way to get fired! ⚠️

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🌟 The Scenario: The Birthday Party 🎂

Imagine you have a list of friends.

• The Update: Your friend "Rahul" just turned 21.
• The Precise Action: You find Rahul's name and change his age to 21. ✅
• The Disaster: You forget to look for Rahul and just shout "EVERYONE IS 21!" Now your list is ruined. ❌

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🎨 Visual Logic: Targeted Modification

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💻 1. The Basic Syntax

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

Example: Update a specific record

-- Scenario: Update phone number for Student 101
UPDATE students
SET phone = '9876543210'
WHERE roll_no = 101;

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💻 2. Updating Multiple Columns 📑

You can change several fields at once by separating them with commas.

-- Scenario: Student moved house and changed email
UPDATE students
SET 
    city = 'Surat',
    email = '[email protected]'
WHERE roll_no = 105;

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💻 3. Updating with Logic (Expressions) ⚙️

You can use the existing value to calculate the new one.

-- Scenario: Give everyone in 'Sales' a 5% raise
UPDATE employees
SET salary = salary * 1.05
WHERE department = 'Sales';

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⚠️ The "No-Where" Danger Zone

If you omit the WHERE clause, EVERY SINGLE ROW in the table will be updated.

-- 💣 DO NOT DO THIS (unless you mean it)
UPDATE students SET status = 'Expelled';
-- Result: Congratulations, you have no students left!

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💡 Pro Tip: The "Safety First" Workflow

"Before running an UPDATE, run a SELECT with the exact same WHERE clause. If the SELECT shows the correct 5 people, then copy that WHERE clause into your UPDATE statement!"

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📈 Learning Path

• ← Back: Multiple Inserts
• Next: DELETE Statement →