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

10.7 LIKE, IN, BETWEEN and NULL

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SELECT name FROM students WHERE name LIKE 'R%';          -- starts with R
SELECT name FROM students WHERE name LIKE '%Bagale';     -- ends with Bagale
SELECT name FROM students WHERE email LIKE '%a%@%';      -- 'a' before @
SELECT name FROM students WHERE name LIKE '_a%';         -- second letter a (_ = one char)
SELECT name, city FROM students WHERE city IN ('Pune', 'Nashik', 'Solapur');
SELECT name, city FROM students WHERE city NOT IN ('Pune');
SELECT name, age FROM students WHERE age BETWEEN 22 AND 25;          -- inclusive
SELECT name, joined_on FROM students WHERE joined_on BETWEEN '2026-03-01' AND '2026-03-31';
SELECT name FROM students WHERE email IS NULL;           -- not "= NULL"! → Raja
SELECT name FROM students WHERE age IS NOT NULL;
Wildcard Meaning Example
% Zero or more characters 'Pu%' → Pune
_ Exactly one character 'R_ja' → Raja

Ravindra Bagale's Tip

Writing WHERE email = NULL gives an empty result, and many students think there's no data. NULL means "unknown" – it can't be compared with =. Always use IS NULL / IS NOT NULL. This question comes up in interviews – remember it.

Practice task

Find students whose name contains "a" as the second letter, students aged 21–24, students from Nagpur or Kolhapur using IN, and students with no email.

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.