UPDATE Statement

Overview

The UPDATE statement modifies existing column values in a database table based on filter conditions.

Learning Objectives

• Modify table attributes using UPDATE ... SET.
• Apply targeted row filters using WHERE.
• Avoid catastrophic un-filtered table updates.

Detailed Concept Explanation

UPDATE modifies column values for existing rows matching a WHERE condition.

The Missing WHERE Danger

If you omit the WHERE clause in an UPDATE query, every single row in the table will be updated!

Code Examples

SQL

-- Increase salary by 10% for employees in department 5
UPDATE employees
SET salary = salary * 1.10
WHERE department_id = 5;

-- Update multiple columns simultaneously
UPDATE users
SET 
  status = 'Active',
  last_login = CURRENT_TIMESTAMP
WHERE user_id = 1042;

Best Practices

• Test with SELECT First: Always run SELECT * FROM table WHERE condition before executing an UPDATE to verify which rows will be affected!

Interview Perspective

Summary

UPDATE ... SET modifies column values in existing rows. Always verify your WHERE filter first!