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SQL Query: 3 Methods for Calculating Cumulative SUM

SQL provides various constructs for calculating cumulative sums, offering flexibility and efficiency in data analysis. In this article, we explore three distinct SQL queries that facilitate the computation of cumulative sums. Each query leverages different SQL constructs to achieve the desired outcome, catering to diverse analytical needs and preferences. Using Window Functions (e.g., PostgreSQL, SQL Server, Oracle) SELECT id, value, SUM(value) OVER (ORDER BY id) AS cumulative_sum  FROM your_table; This query uses the SUM() window function with the OVER clause to calculate the cumulative sum of the value column ordered by the id column. Using Subqueries (e.g., MySQL, SQLite): SELECT t1.id, t1.value, SUM(t2.value) AS cumulative_sum FROM your_table t1 JOIN your_table t2 ON t1.id >= t2.id GROUP BY t1.id, t1.value ORDER BY t1.id; This query uses a self-join to calculate the cumulative sum. It joins the table with itself, matching rows where the id in the first table is greater than or

10 Blockchain Smart Contract Interview Questions

10 Blockchain Smart Contract Interview Questions

Here are the 
top ten interview questions on Blockchain smart contracts. Here you will know about smart-contract, what language and IDE you need to develop. Useful for interviews as well.

1. What is a Smart Contract?

smart contract is an executable code on the blockchain intended to digitally facilitate, verify, validate, and enforce the rules and regulations of an application. Smart contracts allow the performance of credible transactions without third parties. These transactions are trackable and irreversible.

2. Where the smart Contract code resides?

The smart contract is deployed in a sandbox environment and identified by a 160-bit account address like any other participants on the blockchain network. It executes on the virtual machine (VM) on the blockchain node and is identified by an account number.

3. Smart Contract is it API?

Yes, it is like a class. It has methods. These are useful to process transactions in the Blockchain framework.

4. What are the six functions of Smart-contract?

  • It represents a business logic layer for the verification and validation of application-specific conditions.
  • It allows for the specification of rules for operations on the blockchain.
  • It facilitates the implementation of policies for the transfer of assets in a decentralized network.
  • It embeds functions that can be invoked by messages or function calls from participant accounts or other smart contract accounts. These messages and their input parameters, along with additional metadata such as the sender's address and timestamp, result in transactions recorded in the distributed ledger of the blockchain.
  • It acts as the software-based intermediator for decentralized blockchain-based applications.
  • It adds programmability and intelligence to the blockchain through the specification of the parameters of its functions.

5. What are the three key elements of a Smart Contract?

  1. Data
  2. Functions that operate on the data
  3. Rules for operations

6. How does it looks like a Smart Contract?

  • Name of the class
  • Data definitions
  • Function definitions

7. What is the name of the Programming language you use?

Solidity is an object-oriented, high-level language for implementing smart contracts, influenced by C++, Python, and JavaScript. Solidity is statically typed and supports inheritance, libraries, and user-defined types; it also provides many useful features for developing blockchain applications.

8. What is the name of IDE?

Open the Remix web IDE in your browser.

9. Who can access the Smart contract code?

When a smart contract code is deployed on a blockchain, it is accessible to anybody who has a defined identity on that blockchain.

10. Best example of a Blockchain smart contract?

Airline System.


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