UPDATE Statement

The UPDATE Statement

The UPDATE statement modifies existing records in a table.

💡 UPDATE changes the values of one or more columns in existing rows. ALWAYS use a WHERE clause!

Basic Syntax

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

Update a Single Column

UPDATE employees
SET salary = 80000
WHERE first_name = 'Alice' AND last_name = 'Johnson';

Update Multiple Columns

UPDATE employees
SET
    salary = 85000,
    department = 'Senior Engineering'
WHERE id = 1;

Update with Expression

-- Give all Engineering employees a 10% raise
UPDATE employees
SET salary = salary * 1.10
WHERE department = 'Engineering';

Safe Update Pattern

-- Step 1: Preview affected rows
SELECT * FROM employees WHERE department = 'Engineering';

-- Step 2: Run the update
UPDATE employees SET salary = salary * 1.10 WHERE department = 'Engineering';

-- Step 3: Verify the changes
SELECT * FROM employees WHERE department = 'Engineering';

⚠️ Omitting the WHERE clause updates ALL rows. Always test with SELECT first!

✅ Key Takeaways

1. UPDATE modifies existing records in a table
2. Always include a WHERE clause unless updating all rows
3. Preview with SELECT before running UPDATE
4. You can update multiple columns at once
5. Use expressions and subqueries for complex updates