SQL Cheatsheet

✅ SQL Clauses Cheat Sheet! 🧠📘

1️⃣ SELECT – Pick the columns you want

SELECT name, age FROM students;

2️⃣ WHERE – Filter rows based on condition

SELECT * FROM orders WHERE status = 'delivered';

3️⃣ ORDER BY – Sort the results

SELECT * FROM products ORDER BY price DESC;

4️⃣ GROUP BY – Group rows for aggregation

SELECT department, COUNT(*) FROM employees GROUP BY department;

5️⃣ HAVING – Filter groups after aggregation

SELECT department, COUNT(*) FROM employees  
GROUP BY department HAVING COUNT(*) > 5;

6️⃣ LIMIT / TOP – Restrict number of rows 
-- MySQL/PostgreSQL

SELECT * FROM sales LIMIT 10;

-- SQL Server

SELECT TOP 10 * FROM sales;

7️⃣ DISTINCT – Remove duplicates

SELECT DISTINCT city FROM customers;

8️⃣ BETWEEN – Filter within a range

SELECT * FROM invoices WHERE amount BETWEEN 100 AND 500;

9️⃣ IN – Match any from a list

SELECT * FROM users WHERE role IN ('admin', 'manager');

🔟 ALIAS (AS) – Rename columns or tables

SELECT name AS EmployeeName FROM employees;

💡 Tip: Combine clauses for powerful queries!

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20 medium-level SQL interview questions:

1. Write a SQL query to find the second-highest salary.
2. How would you optimize a slow SQL query?
3. What is the difference between INNER JOIN and OUTER JOIN?
4. Write a SQL query to find the top 3 departments with the highest average salary.
5. How do you handle duplicate rows in a SQL query?
6. Write a SQL query to find the employees who have the same name and work in the same department.
7. What is the difference between UNION and UNION ALL?
8. Write a SQL query to find the departments with no employees.
9. How do you use indexing to improve SQL query performance?
10. Write a SQL query to find the employees who have worked for more than 5 years.
11. What is the difference between SUBQUERY and JOIN?
12. Write a SQL query to find the top 2 products with the highest sales.
13. How do you use stored procedures to improve SQL query performance?
14. Write a SQL query to find the customers who have placed an order but have not made a payment.
15. What is the difference between GROUP BY and HAVING?
16. Write a SQL query to find the employees who work in the same department as their manager.
17. How do you use window functions to solve complex queries?
18. Write a SQL query to find the top 3 products with the highest average price.
19. What is the difference between TRUNCATE and DELETE?
20. Write a SQL query to find the employees who have not taken any leave in the last 6 months.

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SQL isn't easy!

It’s the powerful language that helps you manage and manipulate data in databases.

To truly master SQL, focus on these key areas:

0. Understanding the Basics: Get comfortable with SQL syntax, data types, and basic queries like SELECT, INSERT, UPDATE, and DELETE.


1. Mastering Data Retrieval: Learn advanced SELECT statements, including JOINs, GROUP BY, HAVING, and subqueries to retrieve complex datasets.


2. Working with Aggregation Functions: Use functions like COUNT(), SUM(), AVG(), MIN(), and MAX() to summarize and analyze data efficiently.


3. Optimizing Queries: Understand how to write efficient queries and use techniques like indexing and query execution plans for performance optimization.


4. Creating and Managing Databases: Master CREATE, ALTER, and DROP commands for building and maintaining database structures.


5. Understanding Constraints and Keys: Learn the importance of primary keys, foreign keys, unique constraints, and indexes for data integrity.


6. Advanced SQL Techniques: Dive into CASE statements, CTEs (Common Table Expressions), window functions, and stored procedures for more powerful querying.


7. Normalizing Data: Understand database normalization principles and how to design databases to avoid redundancy and ensure consistency.


8. Handling Transactions: Learn how to use BEGIN, COMMIT, and ROLLBACK to manage transactions and ensure data integrity.


9. Staying Updated with SQL Trends: The world of databases evolves—stay informed about new SQL functions, database management systems (DBMS), and best practices.

⏳ With practice, hands-on experience, and a thirst for learning, SQL will empower you to unlock the full potential of data!

You can read detailed article here

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Top 5 SQL Functions

1. SELECT Statement:
   - Function: Retrieving data from one or more tables.
   - Example: SELECT column1, column2 FROM table WHERE condition;

2. COUNT Function:
   - Function: Counts the number of rows that meet a specified condition.
   - Example: SELECT COUNT(column) FROM table WHERE condition;

3. SUM Function:
   - Function: Calculates the sum of values in a numeric column.
   - Example: SELECT SUM(column) FROM table WHERE condition;

4. AVG Function:
   - Function: Computes the average value of a numeric column.
   - Example: SELECT AVG(column) FROM table WHERE condition;

5. GROUP BY Clause:
   - Function: Groups rows that have the same values in specified columns into summary rows.
   - Example: SELECT column, AVG(numeric_column) FROM table GROUP BY column;

These functions are fundamental in SQL and are frequently used for various data manipulation tasks, including data retrieval, aggregation, and analysis.

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SQL interview questions with answers 😄👇

1. Question: What is SQL?

Answer: SQL (Structured Query Language) is a programming language designed for managing and manipulating relational databases. It is used to query, insert, update, and delete data in databases.

2. Question: Differentiate between SQL and MySQL.

Answer: SQL is a language for managing relational databases, while MySQL is an open-source relational database management system (RDBMS) that uses SQL as its language.

3. Question: Explain the difference between INNER JOIN and LEFT JOIN.

Answer: INNER JOIN returns rows when there is a match in both tables, while LEFT JOIN returns all rows from the left table and the matched rows from the right table, filling in with NULLs for non-matching rows.

4. Question: How do you remove duplicate records from a table?

Answer: Use the DISTINCT keyword in a SELECT statement to retrieve unique records. For example: SELECT DISTINCT column1, column2 FROM table;

5. Question: What is a subquery in SQL?

Answer: A subquery is a query nested inside another query. It can be used to retrieve data that will be used in the main query as a condition to further restrict the data to be retrieved.

6. Question: Explain the purpose of the GROUP BY clause.

Answer: The GROUP BY clause is used to group rows that have the same values in specified columns into summary rows, like when using aggregate functions such as COUNT, SUM, AVG, etc.

7. Question: How can you add a new record to a table?

Answer: Use the INSERT INTO statement. For example: INSERT INTO table_name (column1, column2) VALUES (value1, value2);

8. Question: What is the purpose of the HAVING clause?

Answer: The HAVING clause is used in combination with the GROUP BY clause to filter the results of aggregate functions based on a specified condition.

9. Question: Explain the concept of normalization in databases.

Answer: Normalization is the process of organizing data in a database to reduce redundancy and improve data integrity. It involves breaking down tables into smaller, related tables.

10. Question: How do you update data in a table in SQL?

Answer: Use the UPDATE statement to modify existing records in a table. For example: UPDATE table_name SET column1 = value1 WHERE condition;

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14 Days Roadmap to learn SQL

𝗗𝗮𝘆 𝟭: 𝗜𝗻𝘁𝗿𝗼𝗱𝘂𝗰𝘁𝗶𝗼𝗻 𝘁𝗼 𝗗𝗮𝘁𝗮𝗯𝗮𝘀𝗲𝘀 𝗮𝗻𝗱 𝗦𝗤𝗟
Topics to Cover:
- What is SQL?
- Different types of databases (Relational vs. Non-Relational)
- SQL vs. NoSQL
- Overview of SQL syntax
Practice:
- Install a SQL database (e.g., MySQL, PostgreSQL, SQLite)
- Explore an online SQL editor like SQLFiddle or DB Fiddle

𝗗𝗮𝘆 𝟮: 𝗕𝗮𝘀𝗶𝗰 𝗦𝗤𝗟 𝗤𝘂𝗲𝗿𝗶𝗲𝘀
Topics to Cover:
- SELECT statement
- Filtering with WHERE clause
- DISTINCT keyword
Practice:
- Write simple SELECT queries to retrieve data from single table
- Filter records using WHERE clauses

𝗗𝗮𝘆 𝟯: 𝗦𝗼𝗿𝘁𝗶𝗻𝗴 𝗮𝗻𝗱 𝗙𝗶𝗹𝘁𝗲𝗿𝗶𝗻𝗴
Topics to Cover:
- ORDER BY clause
- Using LIMIT/OFFSET for pagination
- Comparison and logical operators
Practice:
- Sort data with ORDER BY
- Apply filtering with multiple conditions use AND/OR

𝗗𝗮𝘆 𝟰: 𝗦𝗤𝗟 𝗙𝘂𝗻𝗰𝘁𝗶𝗼𝗻𝘀 𝗮𝗻𝗱 𝗔𝗴𝗴𝗿𝗲𝗴𝗮𝘁𝗶𝗼𝗻𝘀
Topics to Cover:
- Aggregate functions (COUNT, SUM, AVG, MIN, MAX)
- GROUP BY and HAVING clauses
Practice:
- Perform aggregation on dataset
- Group data and filter groups using HAVING

𝗗𝗮𝘆 𝟱: 𝗪𝗼𝗿𝗸𝗶𝗻𝗴 𝘄𝗶𝘁𝗵 𝗠𝘂𝗹𝘁𝗶𝗽𝗹𝗲 𝗧𝗮𝗯𝗹𝗲𝘀 - 𝗝𝗼𝗶𝗻𝘀
Topics to Cover:
- Introduction to Joins (INNER, LEFT, RIGHT, FULL)
- CROSS JOIN and self-joins
Practice:
- Write queries using different types of JOINs to combine data from multiple table

𝗗𝗮𝘆 𝟲: 𝗦𝘂𝗯𝗾𝘂𝗲𝗿𝗶𝗲𝘀 𝗮𝗻𝗱 𝗡𝗲𝘀𝘁𝗲𝗱 𝗤𝘂𝗲𝗿𝗶𝗲𝘀
Topics to Cover:
- Subqueries in SELECT, WHERE, and FROM clauses
- Correlated subqueries
Practice:
- Write subqueries to filter, aggregate, an select data

𝗗𝗮𝘆 𝟳: 𝗗𝗮𝘁𝗮 𝗠𝗼𝗱𝗲𝗹𝗹𝗶𝗻𝗴 𝗮𝗻𝗱 𝗗𝗮𝘁𝗮𝗯𝗮𝘀𝗲 𝗗𝗲𝘀𝗶𝗴𝗻
Topics to Cover:
- Understanding ERD (Entity Relationship Diagram)
- Normalization (1NF, 2NF, 3NF)
- Primary and Foreign Key
Practice:
- Design a simple database schema and implement it in your database

𝗗𝗮𝘆 𝟴: 𝗠𝗼𝗱𝗶𝗳𝘆𝗶𝗻𝗴 𝗗𝗮𝘁𝗮 - 𝗜𝗡𝗦𝗘𝗥𝗧, 𝗨𝗣𝗗𝗔𝗧𝗘, 𝗗𝗘𝗟𝗘𝗧𝗘
Topics to Cover:
- INSERT INTO statement
- UPDATE and DELETE statement
- Transactions and rollback
Practice:
- Insert, update, and delete records in a table
- Practice transactions with COMMIT and ROLLBACK

𝗗𝗮𝘆 𝟵: 𝗔𝗱𝘃𝗮𝗻𝗰𝗲𝗱 𝗦𝗤𝗟 𝗙𝘂𝗻𝗰𝘁𝗶𝗼𝗻𝘀
Topics to Cover:
- String functions (CONCAT, SUBSTR, etc.)
- Date functions (NOW, DATEADD, DATEDIFF)
- CASE statement
Practice:
- Use string and date function in queries
- Write conditional logic using CASE

𝗗𝗮𝘆 𝟭𝟬: 𝗩𝗶𝗲𝘄𝘀 𝗮𝗻𝗱 𝗜𝗻𝗱𝗲𝘅𝗲𝘀
Topics to Cover:
- Creating and using Views
- Indexes: What they are and how they work
- Pros and cons of using indexes
Practice:
- Create and query views
- Explore how indexes affect query performance

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✅ SQL Learning Checklist 🛠️📊

📚 Foundations
⦁ What is SQL & RDBMS
⦁ SQL Syntax Basics
⦁ Data Types (INT, VARCHAR, DATE, etc.)
⦁ Creating Databases & Tables

🔍 Data Querying
⦁ SELECT, WHERE, ORDER BY
⦁ DISTINCT & LIMIT
⦁ BETWEEN, IN, LIKE
⦁ Logical Operators (AND, OR, NOT)

🧮 Data Aggregation
⦁ COUNT(), SUM(), AVG(), MIN(), MAX()
⦁ GROUP BY & HAVING

🔗 Joins
⦁ INNER JOIN
⦁ LEFT JOIN
⦁ RIGHT JOIN
⦁ FULL OUTER JOIN
⦁ SELF JOIN

🧱 Table Operations
⦁ INSERT INTO
⦁ UPDATE
⦁ DELETE
⦁ ALTER TABLE (ADD/DROP COLUMN)
⦁ DROP TABLE

⚙️ Advanced SQL
⦁ Subqueries
⦁ CASE WHEN statements
⦁ Window Functions (RANK, ROW_NUMBER, etc.)
⦁ CTEs (Common Table Expressions)
⦁ Views & Indexes

🛡️ Data Integrity & Constraints
⦁ PRIMARY KEY, FOREIGN KEY
⦁ UNIQUE, NOT NULL, CHECK
⦁ DEFAULT Values

📁 Projects to Build
⦁ Sales Report Dashboard (SQL backend)
⦁ Employee Database Management
⦁ E-commerce Order Analysis
⦁ Customer Segmentation with SQL

💡 Practice Platforms:
⦁ LeetCode (SQL)
⦁ HackerRank
⦁ Mode Analytics
⦁ SQLZoo

💬 Tap ❤️ for more!

🗄️ 𝗦𝗤𝗟 𝗠𝗮𝘀𝘁𝗲𝗿𝗰𝗹𝗮𝘀𝘀 – 𝗔 𝗚𝘂𝗶𝗱𝗲 𝗳𝗼𝗿 𝗕𝗲𝗴𝗶𝗻𝗻𝗲𝗿𝘀

🔹 𝗪𝗵𝗮𝘁 𝗶𝘀 𝗦𝗤𝗟?
SQL (Structured Query Language) is the standard language used to interact with databases. Whether it’s a small website or a global enterprise, SQL is everywhere.

🔹 𝗪𝗵𝘆 𝗦𝗤𝗟 𝗶𝘀 𝗜𝗺𝗽𝗼𝗿𝘁𝗮𝗻𝘁?
1️⃣ Almost every company uses databases to store information
2️⃣ SQL is essential for Data Analysts, Data Scientists, and Business Analysts
3️⃣ It helps in decision-making by turning raw data into insights
4️⃣ Easy to learn yet extremely powerful

🔹 𝗕𝗮𝘀𝗶𝗰 𝗦𝗤𝗟 𝗖𝗼𝗺𝗺𝗮𝗻𝗱𝘀 𝗬𝗼𝘂 𝗠𝘂𝘀𝘁 𝗞𝗻𝗼𝘄:
✅ CREATE TABLE – Build a new table
✅ SELECT – Extract data from tables
✅ WHERE – Filter records with conditions
✅ ORDER BY – Sort results (ascending/descending)
✅ GROUP BY – Summarize data into groups
✅ JOIN – Combine rows from multiple tables
✅ INSERT, UPDATE, DELETE – Manage records in a table

🔹 𝗔𝗱𝘃𝗮𝗻𝗰𝗲𝗱 𝗦𝗤𝗟 𝗖𝗼𝗻𝗰𝗲𝗽𝘁𝘀:
📌 Subqueries (Nested Queries)
📌 Window Functions (ROW_NUMBER, RANK, DENSE_RANK)
📌 CTEs (Common Table Expressions)
📌 Indexes for performance improvement
📌 Stored Procedures & Triggers

🔹 𝗣𝗿𝗮𝗰𝘁𝗶𝗰𝗮𝗹 𝗨𝘀𝗲 𝗖𝗮𝘀𝗲𝘀 𝗼𝗳 𝗦𝗤𝗟:
✅ Analyzing sales data to find top-selling products
✅ Identifying customer churn with queries
✅ Tracking employee performance
✅ Detecting fraud in banking transactions
✅ Powering dashboards with real-time queries

🔹 𝗧𝗼𝗼𝗹𝘀 𝘁𝗼 𝗣𝗿𝗮𝗰𝘁𝗶𝗰𝗲 𝗦𝗤𝗟:
🔸 MySQL
🔸 PostgreSQL
🔸 Microsoft SQL Server
🔸 Oracle Database
🔸 SQLite

🔹 𝗖𝗮𝗿𝗲𝗲𝗿 𝗦𝗰𝗼𝗽𝗲 𝗶𝗻 𝗦𝗤𝗟:
🚀 SQL is in demand across industries – finance, healthcare, e-commerce, IT, and startups.
💼 Roles that need SQL skills:
– Data Analyst
– Business Analyst
– Data Engineer
– Database Administrator
– Data Scientist

🔹 𝗧𝗶𝗽𝘀 𝘁𝗼 𝗟𝗲𝗮𝗿𝗻 𝗦𝗤𝗟 𝗘𝗳𝗳𝗲𝗰𝘁𝗶𝘃𝗲𝗹𝘆:
1️⃣ Start with simple SELECT queries before moving to complex ones
2️⃣ Solve real-world problems with datasets (Kaggle, Mode Analytics, Hackerrank)
3️⃣ Visualize queries with tools like Power BI or Tableau
4️⃣ Practice daily – SQL is best learned by doing

✨ 𝗕𝗼𝘁𝘁𝗼𝗺 𝗟𝗶𝗻𝗲:
SQL is not just a technical skill — it’s a superpower for anyone working with data. If you want to grow in Data Analytics, SQL should be your first step.

If you want to Excel at using the most used database language in the world, learn these powerful SQL features:

• Wildcards (%, _) – Flexible pattern matching
• Window Functions – ROW_NUMBER(), RANK(), DENSE_RANK(), LEAD(), LAG()
• Common Table Expressions (CTEs) – WITH for better readability
• Recursive Queries – Handle hierarchical data
• STRING Functions – LEFT(), RIGHT(), LEN(), TRIM(), UPPER(), LOWER()
• Date Functions – DATEDIFF(), DATEADD(), FORMAT()
• Pivot & Unpivot – Transform row data into columns
• Aggregate Functions – SUM(), AVG(), COUNT(), MIN(), MAX()
• Joins & Self Joins – Master INNER, LEFT, RIGHT, FULL, SELF JOIN
• Indexing – Speed up queries with CREATE INDEX

Like it if you need a complete tutorial on all these topics! 👍❤️

#sql

Give me 5 minutes, I will tell you

7 ways to get your next job in 3 months.

The situation is tough and talking to your colleague or mentor won’t change a thing. Doing the below 6 things might get you your next opportunity faster

✅ Save this post for future reference

𝟭. 𝗨𝗽𝗱𝗮𝘁𝗲 𝗟𝗶𝗻𝗸𝗲𝗱𝗜𝗻 ‘𝗢𝗽𝗲𝗻 𝗧𝗼 𝗪𝗼𝗿𝗸’ 𝗦𝗲𝘁𝘁𝗶𝗻𝗴

- Use a generic title (Data Engineer) as well as a role-specific title (Azure Data Engineer).
- Select all location types and tech hubs in India.
- Update your current location to Bangalore, Hyderabad, or Noida, as most companies hire from these locations.

𝟮. 𝗦𝗸𝗶𝗹𝗹 𝗘𝗻𝗵𝗮𝗻𝗰𝗲𝗺𝗲𝗻𝘁 𝗮𝗻𝗱 𝗖𝗲𝗿𝘁𝗶𝗳𝗶𝗰𝗮𝘁𝗶𝗼𝗻

- Enhance in-demand skills through courses, certifications and projects to make your profile stand out to employers.

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𝟯. 𝗝𝗼𝗶𝗻 𝗚𝗿𝗼𝘂𝗽𝘀

- Jobs & Internship Opportunities: https://t.iss.one/getjobss
- Data Analyst Jobs: https://t.iss.one/jobs_SQL
- Web Development Jobs: https://t.iss.one/webdeveloperjob
- Data Science Jobs: https://t.iss.one/datasciencej
- Software Engineering Jobs: https://t.iss.one/internshiptojobs
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𝟰. 𝗧𝗿𝗶𝗰𝗸𝘀 𝘁𝗼 𝗴𝗲𝘁 𝗜𝗻𝘁𝗲𝗿𝘃𝗶𝗲𝘄 𝗖𝗮𝗹𝗹𝘀

- Visit the career portals of companies and apply to 10-15 recent openings.
- Cold email to companies/ HRs
- Apply for remote Jobs posted on telegram - https://t.iss.one/jobs_us_uk

𝟱. 𝗔𝘀𝗸 𝗳𝗼𝗿 𝗥𝗲𝗳𝗲𝗿𝗿𝗮𝗹𝘀:

- When asking for a referral, ensure the person passes on your resume explicitly to the hiring manager.
- While asking for referral make sure to send Job id along with resume.

𝟲. 𝘄𝗲𝗯𝘀𝗶𝘁𝗲𝘀 𝘁𝗼 𝗺𝗮𝗸𝗲 𝘆𝗼𝘂𝗿 𝗿𝗲𝘀𝘂𝗺𝗲 𝗯𝗲𝘁𝘁𝗲𝗿:

1. career.io
2. resume.io

𝗝𝗼𝗶𝗻 𝗺𝘆 𝗣𝗲𝗿𝘀𝗼𝗻𝗮𝗹 𝗖𝗵𝗮𝗻𝗻𝗲𝗹𝘀 -
- https://t.iss.one/jobinterviewsprep
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🧠 How much SQL is enough to crack a Data Analyst Interview? 💼💻

📌 Basic Queries
⦁ SELECT, FROM, WHERE
⦁ DISTINCT, IN, BETWEEN, LIKE
⦁ ORDER BY, LIMIT

🔗 Joins and Relations
⦁ INNER JOIN, LEFT/RIGHT/FULL JOIN
⦁ Joining 2–3 tables in real life
⦁ Handling NULLs & duplicates

📊 Aggregate Functions
⦁ COUNT, SUM, AVG, MIN, MAX
⦁ GROUP BY multiple columns
⦁ HAVING vs WHERE filters

🧩 Subqueries & CTEs
⦁ Subqueries in SELECT, WHERE, FROM
⦁ WITH clause for clarity
⦁ Use in data cleaning & filtering

🔍 Window Functions
⦁ ROW_NUMBER, RANK, DENSE_RANK
⦁ LAG, LEAD for time analysis
⦁ PARTITION BY with OVER()

🛠️ Data Manipulation
⦁ CASE WHEN, COALESCE, NULLIF
⦁ Date funcs: DATE_TRUNC, DATEDIFF, NOW()
⦁ String funcs: SUBSTRING, CONCAT, UPPER

📊 Analytics-Focused Practice
⦁ KPI calc: revenue, conversions
⦁ Funnel, retention, user activity
⦁ Ad-hoc queries for business questions

📚 Common Interview Scenarios
⦁ Compare monthly metrics
⦁ Find top N customers/products
⦁ Detect duplicates or anomalies
⦁ Trend analysis with dates

✅ Must-Have Strengths
⦁ Clean, efficient queries
⦁ Clear logic explanation
⦁ Translating business asks to SQL
⦁ Spotting data patterns

💬 Tap ❤️ for more

🗄️ SQL Developer Roadmap

📂 SQL Basics (SELECT, WHERE, ORDER BY)
∟📂 Joins (INNER, LEFT, RIGHT, FULL)
∟📂 Aggregate Functions (COUNT, SUM, AVG)
∟📂 Grouping Data (GROUP BY, HAVING)
∟📂 Subqueries & Nested Queries
∟📂 Data Modification (INSERT, UPDATE, DELETE)
∟📂 Database Design (Normalization, Keys)
∟📂 Indexing & Query Optimization
∟📂 Stored Procedures & Functions
∟📂 Transactions & Locks
∟📂 Views & Triggers
∟📂 Backup & Restore
∟📂 Working with NoSQL basics (optional)
∟📂 Real Projects & Practice
∟✅ Apply for SQL Dev Roles

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🚀 SQL Command Essentials: DDL, DML, DCL, TCL 🚀

● DDL (Data Definition Language)
– CREATE: Make new tables/databases
– ALTER: Change table structure
– DROP: Delete tables/databases
– TRUNCATE: Remove all data, keep structure

● DML (Data Manipulation Language)
– SELECT: Retrieve data
– INSERT: Add data
– UPDATE: Change data
– DELETE: Remove data

● DCL (Data Control Language)
– GRANT: Give access rights
– REVOKE: Remove access rights

● TCL (Transaction Control Language)
– COMMIT: Save changes
– ROLLBACK: Undo changes
– SAVEPOINT: Set a point to rollback to
– BEGIN/END TRANSACTION: Mark begin/end of a transaction

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✅ SQL Constraints! 🛡️

SQL constraints are rules applied to table columns to maintain accurate and reliable data.

🔹 PRIMARY KEY
– Uniquely identifies each row
– No NULLs allowed

🔹 FOREIGN KEY
– Links to a primary key in another table
– Maintains referential integrity

🔹 UNIQUE
– Ensures all values in a column are different

🔹 NOT NULL
– Column must have a value (can’t be empty)

🔹 CHECK
– Restricts the values in a column
👉 Example: CHECK (age >= 18)

🔹 DEFAULT
– Sets a default value if none is provided

Constraints prevent bad data from entering your database 💾

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SQL Cheatsheet 📝

This SQL cheatsheet is designed to be your quick reference guide for SQL programming. Whether you’re a beginner learning how to query databases or an experienced developer looking for a handy resource, this cheatsheet covers essential SQL topics.

1. Database Basics
- CREATE DATABASE db_name;
- USE db_name;

2. Tables
- Create Table: CREATE TABLE table_name (col1 datatype, col2 datatype);
- Drop Table: DROP TABLE table_name;
- Alter Table: ALTER TABLE table_name ADD column_name datatype;

3. Insert Data
- INSERT INTO table_name (col1, col2) VALUES (val1, val2);

4. Select Queries
- Basic Select: SELECT * FROM table_name;
- Select Specific Columns: SELECT col1, col2 FROM table_name;
- Select with Condition: SELECT * FROM table_name WHERE condition;

5. Update Data
- UPDATE table_name SET col1 = value1 WHERE condition;

6. Delete Data
- DELETE FROM table_name WHERE condition;

7. Joins
- Inner Join: SELECT * FROM table1 INNER JOIN table2 ON table1.col = table2.col;
- Left Join: SELECT * FROM table1 LEFT JOIN table2 ON table1.col = table2.col;
- Right Join: SELECT * FROM table1 RIGHT JOIN table2 ON table1.col = table2.col;

8. Aggregations
- Count: SELECT COUNT(*) FROM table_name;
- Sum: SELECT SUM(col) FROM table_name;
- Group By: SELECT col, COUNT(*) FROM table_name GROUP BY col;

9. Sorting & Limiting
- Order By: SELECT * FROM table_name ORDER BY col ASC|DESC;
- Limit Results: SELECT * FROM table_name LIMIT n;

10. Indexes
- Create Index: CREATE INDEX idx_name ON table_name (col);
- Drop Index: DROP INDEX idx_name;

11. Subqueries
- SELECT * FROM table_name WHERE col IN (SELECT col FROM other_table);

12. Views
- Create View: CREATE VIEW view_name AS SELECT * FROM table_name;
- Drop View: DROP VIEW view_name;

✅ Top 7 Must-Prepare Topics for SQL Interviews (2025 Edition) 🗄️

✅ Basic SQL Queries – Master SELECT, FROM, WHERE, ORDER BY, LIMIT
✅ Joins – Understand INNER, LEFT, RIGHT, FULL OUTER JOIN (and when to use them)
✅ Aggregate Functions – Practice COUNT, SUM, AVG, MIN, MAX, GROUP BY, HAVING
✅ Subqueries – Learn nested queries and correlated subqueries
✅ Indexes – Know how to create and use indexes for performance optimization
✅ Window Functions – Understand RANK, ROW_NUMBER, LAG, LEAD (and their use cases)
✅ Data Modification – Practice INSERT, UPDATE, DELETE statements

These are the essentials to ace SQL interviews for data analyst, data engineer, or backend developer roles.

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Data Analyst INTERVIEW QUESTIONS AND ANSWERS
👇👇

1.Can you name the wildcards in Excel?

Ans: There are 3 wildcards in Excel that can ve used in formulas.

Asterisk (*) – 0 or more characters. For example, Ex* could mean Excel, Extra, Expertise, etc.

Question mark (?) – Represents any 1 character. For example, R?ain may mean Rain or Ruin.

Tilde (~) – Used to identify a wildcard character (~, *, ?). For example, If you need to find the exact phrase India* in a list. If you use India* as the search string, you may get any word with India at the beginning followed by different characters (such as Indian, Indiana). If you have to look for India” exclusively, use ~.

Hence, the search string will be india~*. ~ is used to ensure that the spreadsheet reads the following character as is, and not as a wildcard.


2.What is cascading filter in tableau?

Ans: Cascading filters can also be understood as giving preference to a particular filter and then applying other filters on previously filtered data source. Right-click on the filter you want to use as a main filter and make sure it is set as all values in dashboard then select the subsequent filter and select only relevant values to cascade the filters. This will improve the performance of the dashboard as you have decreased the time wasted in running all the filters over complete data source.


3.What is the difference between .twb and .twbx extension?

Ans:
A .twb file contains information on all the sheets, dashboards and stories, but it won’t contain any information regarding data source. Whereas .twbx file contains all the sheets, dashboards, stories and also compressed data sources. For saving a .twbx extract needs to be performed on the data source. If we forward .twb file to someone else than they will be able to see the worksheets and dashboards but won’t be able to look into the dataset.


4.What are the various Power BI versions?

Power BI Premium capacity-based license, for example, allows users with a free license to act on content in workspaces with Premium capacity. A user with a free license can only use the Power BI service to connect to data and produce reports and dashboards in My Workspace outside of Premium capacity. They are unable to exchange material or publish it in other workspaces. To process material, a Power BI license with a free or Pro per-user license only uses a shared and restricted capacity. Users with a Power BI Pro license can only work with other Power BI Pro users if the material is stored in that shared capacity. They may consume user-generated information, post material to app workspaces, share dashboards, and subscribe to dashboards and reports. Pro users can share material with users who don’t have a Power BI Pro subscription while workspaces are at Premium capacity.

ENJOY LEARNING 👍👍

SQL Interview Questions

1. How would you find duplicate records in SQL?
2.What are various types of SQL joins?
3.What is a trigger in SQL?
4.What are different DDL,DML commands in SQL?
5.What is difference between Delete, Drop and Truncate?
6.What is difference between Union and Union all?
7.Which command give Unique values?
8. What is the difference between Where and Having Clause?
9.Give the execution of keywords in SQL?
10. What is difference between IN and BETWEEN Operator?
11. What is primary and Foreign key?
12. What is an aggregate Functions?
13. What is the difference between Rank and Dense Rank?
14. List the ACID Properties and explain what they are?
15. What is the difference between % and _ in like operator?
16. What does CTE stands for?
17. What is database?what is DBMS?What is RDMS?
18.What is Alias in SQL?
19. What is Normalisation?Describe various form?
20. How do you sort the results of a query?
21. Explain the types of Window functions?
22. What is limit and offset?
23. What is candidate key?
24. Describe various types of Alter command?
25. What is Cartesian product?

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