Data Analyst Interview Questions:-

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Explain the ACID properties of SQL | Data Analyst Interview Questions

ACID is an acronym that stands for Atomicity, Consistency, Isolation, and Durability. These properties ensure that a set of database operations (grouped together in a transaction) leave the database in a valid state even in the event of unexpected errors.

Atomicity means that either the entire transaction takes place at once or doesn’t happen at all. There is no midway i.e. transactions do not occur partially. Each transaction is considered as one unit and either runs to completion or is not executed at all.

Consistency means that integrity constraints must be maintained so that the database is consistent before and after the transaction. It refers to the correctness of a database.

Isolation ensures that multiple transactions can occur concurrently without leading to the inconsistency of the database state. Transactions occur independently without interference.

Durability means that once a transaction has been committed, it will remain so, even in the event of power loss, crashes, or errors.

In an e-commerce example, ACID properties ensure that when a customer places an order, the transaction is atomic, and the order is either fully processed or rolled back in case of any failure. The consistency of the database is maintained, ensuring that the product, price, and shipping details are correct and match the database’s constraints. The isolation property ensures that concurrent orders do not interfere with each other, and each order is treated independently. Finally, the durability property ensures that the order details remain intact and do not get lost, even in the case of hardware or software failures.

Solve Data Analyst Interview Questions with given two tables:

ORDERS (Columns: Order_id, Customer_id)
CUSTOMERS (Columns: Customer_id, Customer_name)

Write a SQL query to find complete duplicate rows.

SELECT Order_id, Customer_id, count(*) as count
FROM ORDERS
GROUP BY Order_id, Customer_id
HAVING count(*) >1;

https://onecompiler.com/mysql/43arrn9ys

Find duplicate rows based on the ORDERS table.

SELECT  customer_id, count(*) as count 
FROM orders 
GROUP BY customer_id
HAVING  count(*) > 1;

https://onecompiler.com/mysql/43artpzpx

Find duplicate Order_id.

SELECT order_id, count(*) as count
FROM orders
GROUP BY order_id
HAVING count(*) >1;

https://onecompiler.com/mysql/43artxyac

Fetch data that returns all customer details with Order_id.

SELECT * 
FROM customers c
LEFT JOIN orders o USING (Customer_id);

https://onecompiler.com/mysql/43aru23hn

Fetch data that returns customer details with Order_id, excluding customers without orders

SELECT * 
FROM customers c
LEFT JOIN orders o USING (Customer_id)
Where Order_id is not NULL;

https://onecompiler.com/mysql/43aru4tbm

Given a table PRODUCTS (Columns: product_name, month, Revenue) | Data Analyst Interview Questions

Write a SQL query to return the running sum of revenue for each month

When months are sorted.

SELECT month,  sum(revenue) Over(partition by month order by month ) as sum
FROM products;

https://onecompiler.com/mysql/43arvaffy

When months are not sorted.

SELECT month,  sum(revenue) Over(partition by month ) as sum
FROM products;

https://onecompiler.com/mysql/43aruvr6z

What is the difference between POST and GET API? | Data Analyst Interview Questions

Difference Between POST and GET API Requests

Feature	GET	POST
Purpose	Retrieve data from the server.	Send data to the server (e.g., create or update resources).
Request Data	Passed in the URL parameters.	Passed in the request body.
Visibility	Parameters are visible in the URL.	Data is hidden in the request body.
Caching	Can be cached.	Not cached by default.
Idempotency	Yes – Multiple GET requests return the same response.	No – Repeating a POST request may create duplicate data.
Security	Less secure as data appears in the URL.	More secure since sensitive data (e.g., passwords) is sent in the body.
Use Case Examples	Fetching user details, search queries, getting a product list.	User login, form submissions, adding new records (e.g., registering a new user).

What response do we get when using a GET function? | Data Analyst Interview Questions

A GET request typically returns:

Scenario	HTTP Status Code	Meaning
Success	200 OK	Data is returned successfully.
Not Found	404 Not Found	Resource does not exist.
Unauthorized	401 Unauthorized	Authentication is required.
Forbidden	403 Forbidden	No permission to access the resource.
Server Error	500 Internal Server Error	Issue on the server.

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