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11. MySQL Part 2: UPDATE, ALTER, DELETE, Keys, Constraints and Users

11.1 UPDATE

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UPDATE astitvat aslelya rows madhe value badalto. WHERE shivay UPDATE mhanje sagalya rows badaltat – he lakshat theva.

USE cybercourse;
-- 1. first SELECT the rows you plan to change
SELECT student_id, name, fees_paid FROM students WHERE student_id = 6;
-- 2. then UPDATE with the same WHERE
UPDATE students SET fees_paid = 15000 WHERE student_id = 6;
-- several columns at once
UPDATE students SET city = 'Pune', age = 24 WHERE student_id = 4;
-- calculated update for a group
UPDATE students SET fees_paid = fees_paid + 1000 WHERE city = 'Nagpur';
-- update with a join: add 5 bonus marks for the Networking course
UPDATE enrollments e JOIN courses c ON c.course_id = e.course_id
SET e.score = e.score + 5 WHERE c.course_name = 'Networking';
SELECT ROW_COUNT();    -- how many rows the last statement changed

Why this matters for security

Injection is not only about reading. A vulnerable "update profile" page that builds UPDATE users SET bio='...' WHERE id=5 from input can be abused to change other columns (such as role='admin') or other users' rows. Prepared statements and server-side authorization checks prevent both.

Ravindra Bagale's Tip

Many students write an UPDATE and accidentally press Enter before writing the WHERE – the whole table changes! My rule: first write SELECT ... WHERE ..., look at the rows, then copy that same WHERE to build the UPDATE. And if the data is important, start a transaction first (section 11.2).

Practice task

Increase the fees of all Nashik students by 500, change Zoya's city to Pune, and add 2 marks to every score below 60. Check each change with SELECT before and after.

Extended teaching notes

Why this lesson matters

Use this lesson to strengthen systems you own: understand the risk, practise safely in a lab, then write and apply the fix.

Apply the fix across stacks

Same class of bug, same idea in every language.

Java / Spring Boot

Parameterise queries, encode output, CSRF tokens, limited Actuator, dependency scanning.

ASP.NET Core

EF Core / parameterised SQL, Razor encoding, HTTPS, Data Protection.

Node.js / Express

helmet, parameterised SQL, npm audit, avoid eval and shell concat.

Python / Django / Flask / FastAPI

ORM, autoescape, pip-audit, Bandit; never shell=True with user input.

PHP / Laravel

PDO/Eloquent, Blade escaping, composer audit.

Go / Ruby

database/sql placeholders / ActiveRecord; html/template / ERB escaping; govulncheck / Brakeman.

nginx / Apache / Tomcat

Hide versions, TLS, security headers, least-open ports.

MySQL / PostgreSQL / MongoDB / Redis

Private networks, auth on, least-privilege users, no 0.0.0.0/0.

AWS / Azure / GCP

Roles not long-lived keys, private data stores, cloud audit logs on.

Mini case study

Suppose we are on a purple-team exercise for an Indian mid-size company (sample data). Red notes a technique from this lesson against a lab clone. Blue must show the control that stops it, the log that would have fired, and the ticket that hardens production. That is the standard this course trains you for.

Defender's worksheet (do this today)

  1. Write the lesson title, date and the exact lab target you are allowed to use.
  2. List three owned systems (VMs, apps, or cloud accounts) where this lesson applies.
  3. Run one safe check from the lesson on a lab system only. Paste the command and output.
  4. Write a two-sentence fix you would give a teammate.
  5. Name one related public advisory (CERT-In, CISA, NVD, or a vendor bulletin) with its date.

Indian workplace (sample data)

Suppose we are a junior analyst at Infosys, TCS, Wipro or a fintech SOC in Bengaluru/Pune. Turn this lesson into one checklist item with an owner, a due date and a place to store evidence (ticket + screenshot).

Global practice

Compare your notes with OWASP, CIS Benchmarks, NIST CSF/IR guidance or a cloud Well-Architected security question. Write five lines on what overlaps.

Everyday analogy

Explain the risk and the fix to a family member without jargon. If they can repeat the warning, you understand it well enough to teach juniors.

Key terms

  • Control: a safeguard (patch, config, process, detection).
  • Finding: a weakness backed by evidence.
  • Remediation: the fix plus how you verified it.
  • Scope: systems you have written permission to touch.
  • Least privilege: only the access the task needs.
  • Defence in depth: several layers so one failure does not end the story.

Common mistakes

  • Skipping written permission "just for a quick scan".
  • Practising on hostel, office or public targets without authorisation.
  • Collecting tool output without writing the fix.
  • Copying attack steps onto production to "verify". Defenders verify with versions, configs and patches.
  • Publishing screenshots that contain secrets, cookies or internal hostnames.

Recap

  • Evidence, fix, owner, date.
  • Own lab only.
  • Fix > spectacle.