Handwritten notes · Part 6
SQL Handwritten Notes for Placements (Free PDF)
By Gaurav SharmaPublished
26 pages of handwritten-style SQL and DBMS notes for placements and interviews: joins, NULL traps, order of execution, GROUP BY, subqueries, CTEs, window functions, Nth highest salary, normalization, indexes, ACID and isolation levels, explained in English with Hinglish.
- Pages
- 26
- Format
- A4 PDF
- Language
- English + Hinglish
- Price
- Free by email
What's inside
24 topics, one page each
- 01DBMS, RDBMS, SQL vs NoSQL and the sample tables
- 02DDL, DML, DCL, TCL and DELETE vs TRUNCATE vs DROP
- 03Keys and constraints: primary, foreign, candidate, composite
- 04SELECT, WHERE, LIKE, BETWEEN, ORDER BY, LIMIT
- 05NULL, three-valued logic and the NOT IN trap
- 06Order of execution
- 07GROUP BY, HAVING and WHERE vs HAVING
- 08Joins: inner, left, right, full, cross, with diagrams
- 09Self joins, anti joins and row explosion
- 10Subqueries, correlated subqueries, EXISTS vs IN
- 11CTEs and recursive CTEs
- 12Window functions: ROW_NUMBER, RANK, DENSE_RANK
- 13LAG, LEAD, running totals and moving averages
- 14Nth highest salary and deleting duplicates
- 15Classic interview queries, gaps and islands
- 16UNION vs UNION ALL, CASE and common functions
- 17Indexes: B+ tree, clustered vs non-clustered
- 18Normalization: 1NF, 2NF, 3NF, BCNF
- 19Transactions and ACID
- 20Isolation levels, locks and deadlocks
- 21Views, stored procedures, triggers and SQL injection
- 22Query optimization, EXPLAIN and keyset pagination
- 23Output-based questions
- 24Last-minute revision cheat sheet
SQL rounds in placements test two things: whether you can write the query, and whether you understand what the database does with it. These notes use one small pair of tables throughout, so every example has a concrete answer you can check, and they cover the DBMS theory that interviewers mix into the same round.
What makes these SQL notes different?
- One dataset, every concept. Five employees and three departments, including an employee with no department and a department with no employees, so every join and NULL trap shows up clearly.
- The queries interviewers ask. Nth highest salary, deleting duplicates, top earner per department, employees earning more than their manager, and consecutive-day streaks.
- Theory that goes with it. Order of execution, normalization with a worked example, indexes, ACID and isolation levels with the MySQL and PostgreSQL defaults.
- Hinglish where it helps. NULL, joins, window functions and transactions each get a short Hinglish explanation next to the English definition.
How should you use these SQL notes?
Create the two sample tables in DB Fiddle or a local database, then run each query as you read. Try the output-based questions before checking the answers, and use the last page as a one-page revision sheet.
This is Part 6 of the series. For the backend side of the same interviews, see the Node.js handwritten notes.
FAQ
Questions about these notes
Are these SQL notes really free?
Yes. The full 26-page PDF is free; email me to request the complete PDF. Share it with friends preparing for placements.
Do these notes cover DBMS theory too?
Yes. Keys, normalization from 1NF to BCNF, indexes, transactions, ACID, isolation levels, locks and deadlocks are covered alongside the SQL queries, because placement interviews mix both.
Is the Nth highest salary question covered?
Yes. The notes show it with LIMIT/OFFSET and with DENSE_RANK, explain what to return when there is no Nth salary, and also cover finding and deleting duplicate rows.
Which database do the queries use?
Standard SQL that runs on MySQL and PostgreSQL. Where the two differ, such as integer division, TRUNCATE rollback or default isolation level, the notes say so.
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