35 Most Common SQL Interview Questions 👇👇

1.) Explain order of execution of SQL.
2.) What is difference between where and having?
3.) What is the use of group by?
4.) Explain all types of joins in SQL?
5.) What are triggers in SQL?
6.) What is stored procedure in SQL
7.) Explain all types of window functions?
(Mainly rank, row_num, dense_rank, lead & lag)
8.) What is difference between Delete and Truncate?
9.) What is difference between DML, DDL and DCL?
10.) What are aggregate function and when do we use them? explain with few example.
11.) Which is faster between CTE and Subquery?
12.) What are constraints and types of Constraints?
13.) Types of Keys?
14.) Different types of Operators ?
15.) Difference between Group By and Where?
16.) What are Views?
17.) What are different types of constraints?
18.) What is difference between varchar and nvarchar?
19.) Similar for char and nchar?
20.) What are index and their types?
21.) What is an index? Explain its different types.
22.) List the different types of relationships in SQL.
23.) Differentiate between UNION and UNION ALL.
24.) How many types of clauses in SQL?
25.) What is the difference between UNION and UNION ALL in SQL?
26.) What are the various types of relationships in SQL?
27.) Difference between Primary Key and Secondary Key?
28.) What is the difference between where and having?
29.) Find the second highest salary of an employee?
30.) Write retention query in SQL?
31.) Write year-on-year growth in SQL?
32.) Write a query for cummulative sum in SQL?
33.) Difference between Function and Store procedure ?
34.) Do we use variable in views?
35.) What are the limitations of views?

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35 Important SQL Interview Questions with Detailed Answers:

1. Explain order of execution of SQL.

Order: FROM → JOIN → ON → WHERE → GROUP BY → HAVING → SELECT → DISTINCT → ORDER BY → LIMIT. SQL queries are processed in this logical sequence, not the way they are written.

2. What is difference between WHERE and HAVING?

WHERE filters rows before aggregation, while HAVING filters groups after aggregation.

3. What is the use of GROUP BY?

GROUP BY aggregates data across rows with the same values in specified columns, commonly used with aggregate functions.

4. Explain all types of joins in SQL?

INNER JOIN: Returns matching rows from both tables.
LEFT JOIN: All rows from the left, matched rows from right.
RIGHT JOIN: All rows from the right, matched rows from left.
FULL JOIN: All rows from both, with NULLs where no match.
SELF JOIN: Joins table to itself.
CROSS JOIN: Cartesian product of both tables.

5. What are triggers in SQL?

Triggers are procedural code executed automatically in response to certain events on a table or view (INSERT, UPDATE, DELETE).

6. What is stored procedure in SQL?

A stored procedure is a set of SQL statements saved and executed on demand, useful for modularizing code.

7. Explain all types of window functions?

RANK(): Gives rank with gaps.
DENSE_RANK(): Ranks without gaps.
ROW_NUMBER(): Unique row index.
LEAD(): Access next row.
LAG(): Access previous row.

8. What is difference between DELETE and TRUNCATE?

DELETE: Row-wise deletion, can have WHERE clause, logs each row.
TRUNCATE: Deletes all rows, faster, minimal logging, cannot rollback easily.

9. What is difference between DML, DDL and DCL?

DML: Data Manipulation Language (SELECT, INSERT, UPDATE, DELETE).
DDL: Data Definition Language (CREATE, ALTER, DROP).
DCL: Data Control Language (GRANT, REVOKE).

10. What are aggregate functions?

Functions that return a single value: SUM(), AVG(), COUNT(), MIN(), MAX().

11. Which is faster: CTE or Subquery?

Performance depends on context, but subqueries are sometimes faster as CTEs may be materialized.

12. What are constraints and types?

Rules to maintain data integrity. Types: NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, CHECK, DEFAULT.

13. Types of Keys?

Primary Key
Foreign Key
Unique Key
Composite Key
Candidate Key

14. Different types of Operators?

Arithmetic: +, -, *, /
Comparison: =, <>, >, <, >=, <=
Logical: AND, OR, NOT
Bitwise, LIKE, IN, BETWEEN

15. Difference between GROUP BY and WHERE?

WHERE filters before aggregation. GROUP BY groups after filtering.

16. What are Views?

Virtual tables based on SQL queries. They store only query definition.

17. What are different types of constraints?

Same as Q12: NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, CHECK, DEFAULT.

18. What is difference between VARCHAR and NVARCHAR?

VARCHAR: ASCII, 1 byte per char.
NVARCHAR: Unicode, 2 bytes per char, supports multiple languages.

19. Similarity for CHAR and NCHAR?

CHAR: Fixed-length ASCII.
NCHAR: Fixed-length Unicode.

20. What are indexes and their types?

Used for faster retrieval.

Types:
- Clustered
- Non-clustered
- Unique
- Composite
- Full-text

21. What is an index? Explain its types.

Same as above. Indexes speed up queries by creating pointers to data.

22. List different types of relationships in SQL.

One-to-One
One-to-Many
Many-to-Many

23. Differentiate between UNION and UNION ALL.

UNION: Removes duplicates.
UNION ALL: Includes duplicates.

24. How many types of clauses in SQL?

Common clauses: SELECT, FROM, WHERE, GROUP BY, HAVING, ORDER BY, LIMIT, OFFSET, JOIN, ON.

25. What is the difference between UNION and UNION ALL in SQL?

Same as Q23.

26. What are various types of relationships in SQL?
Same as Q22.

27. Difference between Primary Key and Secondary Key?

Primary Key: Uniquely identifies rows.
Secondary Key: May not be unique, used for lookup.

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150 SQL queries for practice ❤️

Here are some interview questions for both freshers and experienced applying for a data analyst #SQL

Analyst role:

#ForFreshers:
1. What is SQL, and why is it important in data analysis?
2. Explain the difference between a database and a table.
3. What are the basic SQL commands for data retrieval?
4. How do you retrieve all records from a table named "Employees"?
5. What is a primary key, and why is it important in a database?
6. What is a foreign key, and how is it used in SQL?
7. Describe the difference between SQL JOIN and SQL UNION.
8. How do you write a SQL query to find the second-highest salary in a table?
9. What is the purpose of the GROUP BY clause in SQL?
10. Can you explain the concept of normalization in SQL databases?
11. What are the common aggregate functions in SQL, and how are they used?

ForExperiencedCandidates:

1. Describe a scenario where you had to optimize a slow-running SQL query. How did you approach it?
2. Explain the differences between SQL Server, MySQL, and Oracle databases.
3. Can you describe the process of creating an index in a SQL database and its impact on query performance?
4. How do you handle data quality issues when performing data analysis with SQL?
5. What is a subquery, and when would you use it in SQL? Give an example of a complex SQL query you've written to extract specific insights from a database.
6. How do you handle NULL values in SQL, and what are the challenges associated with them?
7. Explain the ACID properties of a database and their importance.
8. What are stored procedures and triggers in SQL, and when would you use them?
9. Describe your experience with ETL (Extract, Transform, Load) processes using SQL.
10. Can you explain the concept of query optimization in SQL, and what techniques have you used for optimization?

Enjoy Learning 👍👍

𝐒𝐨𝐦𝐞 𝐁𝐞𝐬𝐭 𝐩𝐫𝐚𝐜𝐭𝐢𝐜𝐞𝐬 𝐭𝐨 𝐡𝐞𝐥𝐩 𝐲𝐨𝐮 𝐨𝐩𝐭𝐢𝐦𝐢𝐳𝐞 𝐲𝐨𝐮𝐫 𝐒𝐐𝐋 𝐪𝐮𝐞𝐫𝐢𝐞𝐬:

1. Simplify Joins

• Decompose complex joins into simpler, more manageable queries when possible.
• Index columns that are used as foreign keys in joins to enhance join performance.

2. Query Structure Optimization

• Apply WHERE clauses as early as possible to filter out rows before they are processed further.
• Utilize LIMIT or TOP clauses to restrict the number of rows returned, which can significantly reduce processing time.

3. Partition Large Tables

• Divide large tables into smaller, more manageable partitions.
• Ensure that each partition is properly indexed to maintain query performance.

4. Optimize SELECT Statements

• Limit the columns in your SELECT clause to only those you need. Avoid using SELECT * to prevent unnecessary data retrieval.
• Prefer using EXISTS over IN for subqueries to improve query performance.

5. Use Temporary Tables Wisely

• Temporary Tables: Use temporary tables to save intermediate results when you have a complex query. This helps break down a complicated query into simpler steps, making it easier to manage and faster to run.

6. Optimize Table Design

• Normalize your database schema to eliminate redundant data and improve consistency.
• Consider denormalization for read-heavy systems to reduce the number of joins needed.

7. Avoid Correlated Subqueries

• Replace correlated subqueries with joins or use derived tables to improve performance.
• Correlated subqueries can be very inefficient as they are executed multiple times.

8. Use Stored Procedures:

• Put complicated database tasks into stored procedures. These are pre-written sets of instructions saved in the database. They make your queries run faster because the database doesn’t have to figure out how to execute them each time

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SQL Interview Questions asked by Urban Company:-

Question 1: Monthly Revenue Trends by Category

Scenario: Analyze monthly revenue trends for each product category.
Table:
1. transactions (Transaction_id, Product_id, Amount_spent, Transaction_date),

2. products (Product_id, Category)

Challenge: Write a SQL query to calculate the total revenue for each category on a monthly basis and identify the top 3 categories with the highest revenue growth month-over-month.

Question 2: Customer Retention Analysis
Scenario: Determine the retention rate of customers.

Table:
1. customer_visits (Customer_id, Visit_date)

Challenge: Write a SQL query to calculate the retention rate of customers month-over-month for the past year, identifying the percentage of customers who return the following month.

Question 3: Product Affinity Analysis
Scenario: Identify products that are frequently bought together.

Table:
1. order_details (Order_id, Product_id, Quantity)

Challenge: Write a SQL query to find pairs of products that are frequently bought together. Include the count of how many times each pair appears in the same order and rank them by frequency.

Question 4: Customer Purchase Segmentation

Scenario: Segment customers based on their purchase behavior.
Table:
1. purchases (Customer_id, Product_id, Amount_spent, Purchase_date)

Challenge: Write a SQL query to segment customers into different groups based on their total spending and purchase frequency in the last year. Classify them into categories like 'High Spenders', 'Medium Spenders', and 'Low Spenders'.

Question 5: Anomaly Detection in Transactions

Scenario: Detect anomalies in transaction amounts.
Table:
1. transactions (Transaction_id, Customer_id, Amount_spent, Transaction_date)

Challenge: Write a SQL query to identify transactions that deviate significantly from the customer's average spending. Flag transactions that are more than three standard deviations away from the mean spending amount for each customer.

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Basics of SQL 👇👇

1. SQL (Structured Query Language) is a standard programming language used for managing and manipulating relational databases.

2. SQL operates through simple, declarative statements. These statements are used to perform tasks such as querying data, updating data, inserting data, and deleting data from a database.

3. The basic SQL commands include SELECT, INSERT, UPDATE, DELETE, CREATE, and DROP.

4. The SELECT statement is used to retrieve data from a database. It allows you to specify the columns you want to retrieve and filter the results using conditions.

5. The INSERT statement is used to add new records to a table in a database.

6. The UPDATE statement is used to modify existing records in a table.

7. The DELETE statement is used to remove records from a table.

8. The CREATE statement is used to create new tables, indexes, or views in a database.

9. The DROP statement is used to remove tables, indexes, or views from a database.

10. SQL also supports various operators such as AND, OR, NOT, LIKE, IN, BETWEEN, and ORDER BY for filtering and sorting data.

11. SQL also allows for the use of functions and aggregate functions like SUM, AVG, COUNT, MIN, and MAX to perform calculations on data.

12. SQL statements are case-insensitive but conventionally written in uppercase for readability.

13. SQL databases are relational databases that store data in tables with rows and columns. Tables can be related to each other through primary and foreign keys.

14. SQL databases use transactions to ensure data integrity and consistency. Transactions can be committed (saved) or rolled back (undone) based on the success of the operations.

15. SQL databases support indexing for faster data retrieval and performance optimization.

16. SQL databases can be queried using tools like MySQL, PostgreSQL, Oracle Database, SQL Server, SQLite, and others.

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DATA ANALYST Interview Questions (0-3 yr) (SQL, Power BI)

👉 Power BI:

Q1: Explain step-by-step how you will create a sales dashboard from scratch.

Q2: Explain how you can optimize a slow Power BI report.

Q3: Explain Any 5 Chart Types and Their Uses in Representing Different Aspects of Data.

👉SQL:

Q1: Explain the difference between RANK(), DENSE_RANK(), and ROW_NUMBER() functions using example.

Q2 – Q4 use Table: employee (EmpID, ManagerID, JoinDate, Dept, Salary)

Q2: Find the nth highest salary from the Employee table.

Q3: You have an employee table with employee ID and manager ID. Find all employees under a specific manager, including their subordinates at any level.

Q4: Write a query to find the cumulative salary of employees department-wise, who have joined the company in the last 30 days.

Q5: Find the top 2 customers with the highest order amount for each product category, handling ties appropriately. Table: Customer (CustomerID, ProductCategory, OrderAmount)

👉Behavioral:

Q1: Why do you want to become a data analyst and why did you apply to this company?

Q2: Describe a time when you had to manage a difficult task with tight deadlines. How did you handle it?

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Top 10 Advanced SQL Interview Questions and Answers 

1. What is a Common Table Expression (CTE), and when would you use it? 
   A Common Table Expression (CTE) is a temporary result set that can be referred to within a SELECT, INSERT, UPDATE, or DELETE statement. 
   Example: 
 

   WITH SalesCTE AS (
       SELECT SalespersonID, SUM(SalesAmount) AS TotalSales
       FROM Sales
       GROUP BY SalespersonID
   )
   SELECT * FROM SalesCTE WHERE TotalSales > 5000;
   

2. How do you optimize a query with a large dataset? 
   - Use proper indexes. 
   - Avoid SELECT *; only retrieve required columns. 
   - Break down complex queries using temporary tables or CTEs. 
   - Analyze query execution plans. 

3. What is the difference between RANK(), DENSE_RANK(), and ROW_NUMBER()? 
   - RANK(): Skips ranking if there’s a tie (e.g., 1, 2, 2, 4). 
   - DENSE_RANK(): Does not skip ranks after a tie (e.g., 1, 2, 2, 3). 
   - ROW_NUMBER(): Assigns unique numbers sequentially, regardless of ties. 

4. How do you find duplicate records in a table? 
 

   SELECT ColumnName, COUNT(*)
   FROM TableName
   GROUP BY ColumnName
   HAVING COUNT(*) > 1;
   

5. What is the difference between INNER JOIN and LEFT JOIN? 
   - INNER JOIN: Returns records that match in both tables. 
   - LEFT JOIN: Returns all records from the left table, and matching records from the right table (NULL if no match). 

6. Explain window functions and provide an example. 
   Window functions operate on a set of rows related to the current row, without collapsing them into a single output. 
   Example: 
 

   SELECT EmployeeID, Salary, 
          RANK() OVER (PARTITION BY DepartmentID ORDER BY Salary DESC) AS Rank
   FROM Employees;
   

7. What are the different types of indexes in SQL? 
   - Clustered Index: Reorders the data physically in the table. 
   - Non-Clustered Index: Creates a separate structure for data retrieval. 
   - Unique Index: Ensures no duplicate values in the column. 

8. How do you handle NULL values in SQL? 
   - Use COALESCE() or ISNULL() to replace NULL values. 
   - Filter with IS NULL or IS NOT NULL in WHERE clauses. 
   Example: 
 

   SELECT COALESCE(PhoneNumber, 'N/A') AS ContactNumber FROM Customers;
   

9. What is the difference between DELETE and TRUNCATE? 
   - DELETE: Removes specific rows, can use WHERE clause, and logs individual row deletions. 
   - TRUNCATE: Removes all rows, faster, and resets table identity. 

10. How do you use a CASE statement in SQL? 
  

    SELECT ProductName,
           CASE 
               WHEN Quantity > 100 THEN 'High Stock'
               WHEN Quantity BETWEEN 50 AND 100 THEN 'Medium Stock'
               ELSE 'Low Stock'
           END AS StockStatus
    FROM Products;
   

🎯 Top 20 SQL Interview Questions You Must Know

SQL is one of the most in-demand skills for Data Analysts.

Here are 20 SQL interview questions that frequently appear in job interviews.

📌 Basic SQL Questions

1️⃣ What is the difference between INNER JOIN and LEFT JOIN?
2️⃣ How does GROUP BY work, and why do we use it?
3️⃣ What is the difference between HAVING and WHERE?
4️⃣ How do you remove duplicate rows from a table?
5️⃣ What is the difference between RANK(), DENSE_RANK(), and ROW_NUMBER()?

📌 Intermediate SQL Questions

6️⃣ How do you find the second highest salary from an Employee table?
7️⃣ What is a Common Table Expression (CTE), and when should you use it?
8️⃣ How do you identify missing values in a dataset using SQL?
9️⃣ What is the difference between UNION and UNION ALL?
🔟 How do you calculate a running total in SQL?

📌 Advanced SQL Questions

1️⃣1️⃣ How does a self-join work? Give an example.
1️⃣2️⃣ What is a window function, and how is it different from GROUP BY?
1️⃣3️⃣ How do you detect and remove duplicate records in SQL?
1️⃣4️⃣ Explain the difference between EXISTS and IN.
1️⃣5️⃣ What is the purpose of COALESCE()?

📌 Real-World SQL Scenarios

1️⃣6️⃣ How do you optimize a slow SQL query?
1️⃣7️⃣ What is indexing in SQL, and how does it improve performance?
1️⃣8️⃣ Write an SQL query to find customers who have placed more than 3 orders.
1️⃣9️⃣ How do you calculate the percentage of total sales for each category?
2️⃣0️⃣ What is the use of CASE statements in SQL?

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Here are some commonly asked SQL interview questions along with brief answers:

1. What is SQL?
- SQL stands for Structured Query Language, used for managing and manipulating relational databases.

2. What are the types of SQL commands?
- SQL commands can be broadly categorized into four types: Data Definition Language (DDL), Data Manipulation Language (DML), Data Control Language (DCL), and Transaction Control Language (TCL).

3. What is the difference between CHAR and VARCHAR data types?
- CHAR is a fixed-length character data type, while VARCHAR is a variable-length character data type. CHAR will always occupy the same amount of storage space, while VARCHAR will only use the necessary space to store the actual data.

4. What is a primary key?
- A primary key is a column or a set of columns that uniquely identifies each row in a table. It ensures data integrity by enforcing uniqueness and can be used to establish relationships between tables.

5. What is a foreign key?
- A foreign key is a column or a set of columns in one table that refers to the primary key in another table. It establishes a relationship between two tables and ensures referential integrity.

6. What is a JOIN in SQL?
- JOIN is used to combine rows from two or more tables based on a related column between them. There are different types of JOINs, including INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.

7. What is the difference between INNER JOIN and OUTER JOIN?
- INNER JOIN returns only the rows that have matching values in both tables, while OUTER JOIN (LEFT, RIGHT, FULL) returns all rows from one or both tables, with NULL values in columns where there is no match.

8. What is the difference between GROUP BY and ORDER BY?
- GROUP BY is used to group rows that have the same values into summary rows, typically used with aggregate functions like SUM, COUNT, AVG, etc., while ORDER BY is used to sort the result set based on one or more columns.

9. What is a subquery?
- A subquery is a query nested within another query, used to return data that will be used in the main query. Subqueries can be used in SELECT, INSERT, UPDATE, and DELETE statements.

10. What is normalization in SQL?
- Normalization is the process of organizing data in a database to reduce redundancy and dependency. It involves dividing large tables into smaller tables and defining relationships between them to improve data integrity and efficiency.

Around 90% questions will be asked from sql in data analytics interview, so please make sure to practice SQL skills using websites like stratascratch. ☺️💪

Scenario based  Interview Questions & Answers for Data Analyst

1. Scenario: You are working on a SQL database that stores customer information. The database has a table called "Orders" that contains order details. Your task is to write a SQL query to retrieve the total number of orders placed by each customer.
  Question:
  - Write a SQL query to find the total number of orders placed by each customer.
Expected Answer:
    SELECT CustomerID, COUNT(*) AS TotalOrders
    FROM Orders
    GROUP BY CustomerID;

2. Scenario: You are working on a SQL database that stores employee information. The database has a table called "Employees" that contains employee details. Your task is to write a SQL query to retrieve the names of all employees who have been with the company for more than 5 years.
  Question:
  - Write a SQL query to find the names of employees who have been with the company for more than 5 years.
Expected Answer:
    SELECT Name
    FROM Employees
    WHERE DATEDIFF(year, HireDate, GETDATE()) > 5;

Power BI Scenario-Based Questions

1. Scenario: You have been given a dataset in Power BI that contains sales data for a company. Your task is to create a report that shows the total sales by product category and region.
    Expected Answer:
    - Load the dataset into Power BI.
    - Create relationships if necessary.
    - Use the "Fields" pane to select the necessary fields (Product Category, Region, Sales).
    - Drag these fields into the "Values" area of a new visualization (e.g., a table or bar chart).
    - Use the "Filters" pane to filter data as needed.
    - Format the visualization to enhance clarity and readability.

2. Scenario: You have been asked to create a Power BI dashboard that displays real-time stock prices for a set of companies. The stock prices are available through an API.
  Expected Answer:
    - Use Power BI Desktop to connect to the API.
    - Go to "Get Data" > "Web" and enter the API URL.
    - Configure the data refresh settings to ensure real-time updates (e.g., setting up a scheduled refresh or using DirectQuery if supported).
    - Create visualizations using the imported data.
    - Publish the report to the Power BI service and set up a data gateway if needed for continuous refresh.

3. Scenario: You have been given a Power BI report that contains multiple visualizations. The report is taking a long time to load and is impacting the performance of the application.
    Expected Answer:
    - Analyze the current performance using Performance Analyzer.
    - Optimize data model by reducing the number of columns and rows, and removing unnecessary calculations.
    - Use aggregated tables to pre-compute results.
    - Simplify DAX calculations.
    - Optimize visualizations by reducing the number of visuals per page and avoiding complex custom visuals.
    - Ensure proper indexing on the data source.

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📖 Visualizing a SQL query

Database keys

Database keys are essential for organizing and managing data effectively. In this post, we'll explore ten key concepts that every IT professional should know.

1. 🗝 𝗣𝗿𝗶𝗺𝗮𝗿𝘆 𝗞𝗲𝘆
- A unique identifier for each record in a table.
- Cannot be null.
- Ensures that each row is unique.

2. 🌉 𝗙𝗼𝗿𝗲𝗶𝗴𝗻 𝗞𝗲𝘆
- A field in one table that refers to the Primary Key of another table.
- Establishes relationships between tables.

3. 🧩 𝗖𝗼𝗺𝗽𝗼𝘀𝗶𝘁𝗲 𝗞𝗲𝘆
- A combination of two or more columns that uniquely identifies each record.
- Useful when a single column can't uniquely identify a record.

4. 💪 𝗦𝘂𝗽𝗲𝗿 𝗞𝗲𝘆
- One or more columns that can uniquely identify a record.
- A Primary Key is a type of Super Key.

5. 🏅 𝗖𝗮𝗻𝗱𝗶𝗱𝗮𝘁𝗲 𝗞𝗲𝘆
- A column or set of columns that could be the Primary Key.
- Must be unique.

6. 🔍 𝗨𝗻𝗶𝗾𝘂𝗲 𝗞𝗲𝘆
- Ensures uniqueness for a column or column combination.
- Similar to Primary Key but allows one null value.

7. 🛤 𝗔𝗹𝘁𝗲𝗿𝗻𝗮𝘁𝗲 𝗞𝗲𝘆
- A Candidate Key that isn't the Primary Key.
- Another option for a unique identifier.

8. 🍃 𝗡𝗮𝘁𝘂𝗿𝗮𝗹 𝗞𝗲𝘆
- A key that's a natural part of the data, like an email address.

9. 🎭 𝗦𝘂𝗿𝗿𝗼𝗴𝗮𝘁𝗲 𝗞𝗲𝘆
- An artificial key created when no natural unique identifier exists.

10. 🔑 𝗦𝗲𝗰𝗼𝗻𝗱𝗮𝗿𝘆 𝗞𝗲𝘆
- Used for data retrieval, not identification.
- Helps create non-clustered indexes.

1. What is a Self-Join?

A self-join is a type of join that can be used to connect two tables. As a result, it is a unary relationship. Each row of the table is attached to itself and all other rows of the same table in a self-join. As a result, a self-join is mostly used to combine and compare rows from the same database table.


2. What is OLTP?

OLTP, or online transactional processing, allows huge groups of people to execute massive amounts of database transactions in real time, usually via the internet. A database transaction occurs when data in a database is changed, inserted, deleted, or queried.


3. What is the difference between joining and blending in Tableau?

Joining term is used when you are combining data from the same source, for example, worksheet in an Excel file or tables in Oracle databaseWhile blending requires two completely defined data sources in your report.


4. How to prevent someone from copying the cell from your worksheet in excel?

If you want to protect your worksheet from being copied, go into Menu bar > Review > Protect sheet > Password.

By entering password you can prevent your worksheet from getting copied.


5. What are the different integrity rules present in the DBMS?

The different integrity rules present in DBMS are as follows:
Entity Integrity: This rule states that the value of the primary key can never be NULL. So, all the tuples in the column identified as the primary key should have a value.
Referential Integrity: This rule states that either the value of the foreign key is NULL or it should be the primary key of any other relation.

Types of Databases

SQL Interview Questions for 0-1 year of Experience (Asked in Top Product-Based Companies).

Sharpen your SQL skills with these real interview questions!

Q1. Customer Purchase Patterns -
You have two tables, Customers and Purchases: CREATE TABLE Customers ( customer_id INT PRIMARY KEY, customer_name VARCHAR(255) ); CREATE TABLE Purchases ( purchase_id INT PRIMARY KEY, customer_id INT, product_id INT, purchase_date DATE );
Assume necessary INSERT statements are already executed.
Write an SQL query to find the names of customers who have purchased more than 5 different products within the last month. Order the result by customer_name.

Q2. Call Log Analysis -
Suppose you have a CallLogs table: CREATE TABLE CallLogs ( log_id INT PRIMARY KEY, caller_id INT, receiver_id INT, call_start_time TIMESTAMP, call_end_time TIMESTAMP );
Assume necessary INSERT statements are already executed.
Write a query to find the average call duration per user. Include only users who have made more than 10 calls in total. Order the result by average duration descending.

Q3. Employee Project Allocation - Consider two tables, Employees and Projects:
CREATE TABLE Employees ( employee_id INT PRIMARY KEY, employee_name VARCHAR(255), department VARCHAR(255) ); CREATE TABLE Projects ( project_id INT PRIMARY KEY, lead_employee_id INT, project_name VARCHAR(255), start_date DATE, end_date DATE );
Assume necessary INSERT statements are already executed.
The goal is to write an SQL query to find the names of employees who have led more than 3 projects in the last year. The result should be ordered by the number of projects led.