SQL · Lesson 6 of 8

INSERT, UPDATE & DELETE

Adding, changing and removing rows safely.

These statements change data:

INSERT INTO jobs (title, city) VALUES ('Tester', 'Kochi'); — add a row. Name the columns so the statement survives table changes.
UPDATE jobs SET salary_lpa = 4 WHERE id = 1; — change rows.
DELETE FROM jobs WHERE id = 9; — remove rows.

Always write the WHERE clause first. UPDATE or DELETE without WHERE changes every row. In real systems, run a SELECT with the same WHERE to preview, and use transactions (BEGIN … COMMIT / ROLLBACK).

Don't worry here — the sample database is rebuilt every time you press Run.

Try it yourself

Code editor

Press Run to see the results.

Runs on a small fictional sample database (companies, jobs) that is rebuilt on every run, so you can't break anything.

Key points

Name columns in INSERT.
Never run UPDATE/DELETE without WHERE by accident.
Preview with SELECT; use transactions in production.

Quick check

What happens with DELETE FROM jobs; (no WHERE)?

Nothing The table is dropped Every row is deleted Only the first row is deleted

Practice task

Add a new company in 'Cyberpark' with 40 employees, then show all Cyberpark companies.

Interview corner

DELETE vs TRUNCATE vs DROP?

DELETE removes chosen rows and can be rolled back. TRUNCATE quickly removes all rows (not available in SQLite). DROP removes the whole table and its structure.

What is a transaction and what does ACID mean?

A group of statements that succeed or fail together. ACID: Atomicity, Consistency, Isolation, Durability.