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10. MySQL Part 1: Install, Create, Insert and SELECT

10.5 SELECT Basics and WHERE

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SELECT mhanje prashna vicharne. WHERE mhanje filter – kontya rows pahijet.

SELECT * FROM students;                              -- all columns (avoid in apps)
SELECT name, city FROM students;                     -- chosen columns
SELECT name, fees_paid FROM students WHERE city = 'Pune';
SELECT name, age FROM students WHERE age > 25;
SELECT name FROM students WHERE city = 'Nagpur' AND fees_paid >= 10000;
SELECT name FROM students WHERE city = 'Pune' OR city = 'Nashik';
SELECT name FROM students WHERE NOT city = 'Pune';
SELECT name FROM students WHERE city <> 'Pune';      -- same as above
Operator Meaning
=, <> or != Equal, not equal
>, <, >=, <= Comparisons
AND, OR, NOT Combine conditions (use brackets to be clear)

Sample output of SELECT name, fees_paid FROM students WHERE city = 'Pune';

name fees_paid
Ravindra Bagale 15000.00
Shraddha Bagale 15000.00
Rani 15000.00

Why this matters for security

The classic injection ' OR '1'='1 works because OR with an always-true condition makes the WHERE clause match every row – for a login query, that means "logged in without a password". Once you understand WHERE, you understand why that payload works.

Ravindra Bagale's Tip

If you use AND and OR together without brackets, you get the wrong rows – many students fall into this trap. AND is evaluated first. If in doubt, always use brackets: WHERE (city='Pune' OR city='Nashik') AND age > 25.

Practice task

Show students from Nagpur; students older than 24 who paid 15000; and students not from Pune – three separate queries.

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.

Try it Yourself

Change the code and press Run. Nothing is saved, so you can experiment freely. Reset brings back the example.

SELECT * FROM orders;
SELECT customer, city, amount, currency
FROM orders
WHERE currency = '₹';
SELECT id, customer, course, order_date
FROM orders
WHERE course = 'SQL Basics' AND order_date >= '2026-09-05';