DataBolt

All Lessons

Introduction to SQL

SQL Lesson 1: Your Sample Database

SQL Lesson 2: SELECT — Reading data

SQL Lesson 3: WHERE — Filtering rows

SQL Lesson 4: AND, OR, NOT

SQL Lesson 5: BETWEEN, IN, LIKE

SQL Lesson 6: NULL — The Mystery Value

SQL Lesson 7: ORDER BY

SQL Lesson 8: LIMIT & OFFSET

SQL Lesson 9: Aggregate Functions

SQL Lesson 10: GROUP BY

SQL Lesson 11: HAVING

SQL Lesson 12: INNER JOINs

SQL Lesson 13: LEFT JOINs

SQL Lesson 14: RIGHT JOINs

SQL Lesson 15: SELF JOINs

SQL Lesson 16: UNION JOINs

SQL Lesson 17: Joining Multiple Tables

SQL Lesson 18: Subqueries

SQL Lesson 19: CTEs (WITH)

SQL Lesson 20: CASE Statements

SQL Lesson 21: Window Functions

SQL Lesson 22: String Functions

SQL Lesson 23: Date & Time Functions

SQL Lesson 24: INSERT, UPDATE, DELETE

SQL Lesson 25: CREATE TABLE & DDL

SQL Lesson 26: Indexes & Performance

SQL Lesson 27: Transactions & ACID

SQL Lesson 28: SQL Execution Order

SQL Lesson 29: 50 Practice Problems

CHAPTER 25

INSERT, UPDATE, DELETE

Modifying data — the right way, safely.

IN THIS CHAPTER

adding single and multiple rows
UPDATE — modifying existing data with WHERE
DELETE — removing rows safely
The golden rule: always test with SELECT first

21.1 - INSERT

SQL

INSERT INTO employees (name, department, salary, hire_date)
VALUES ('Nisha', 'IT', 71000, '2024-03-01');
-- Multiple rows at once
INSERT INTO employees (name, department, salary, hire_date) VALUES
    ('Akash', 'Sales', 58000, '2024-04-01'),
    ('Pooja', 'HR', 62000, '2024-04-15');

21.2 - UPDATE

10% raise for all IT employees

UPDATE employees
SET salary = salary * 1.10
WHERE department = 'IT';

💡 Watch Out: Always include a WHERE clause in UPDATE. 'UPDATE employees SET salary = salary * 1.10' with no WHERE gives everyone a raise — not just IT. This is called a 'fat finger' mistake and it has caused real production incidents at major companies.

21.3 - DELETE

SQL

-- Safe workflow: SELECT first, then DELETE
SELECT * FROM employees WHERE salary < 50000;        -- verify what
will be deleted
DELETE FROM employees WHERE salary < 50000;          -- then delete

✅ Pro Tips: Wrap destructive operations in a transaction: START TRANSACTION; DELETE ...; ROLLBACK; — verify, then COMMIT when satisfied. This is standard practice at any serious engineering team.

Exercise 👇

Exercise:

Tasks

1.👉Insert a new employee Rohit into the table.

2.Update Priya's salary to 80000.

3.Change Rahul's department to Marketing.

4.Delete the employee with emp_id 8.

5.Insert a new employee Neha using column names.

6.Delete all employees from HR department.

Stuck? Read this task's