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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 Kafka Interview Questions That Recently Asked

10 Kafka Interview Questions That Recently Asked

Kafka Interview Questions

Here're ten interview questions that were asked during Kafka's interview.  These are useful to update your knowledge.

1. What is Kafka?

Kafka is a framework of Publisher and Subscribe. It reads messages from the Producer and allows them to read by Subscribers. It keeps store all the producer messages in the form of topics (underlying partitions). It also maintains logs.

2. What is a Consumer group?

Each consumer is part of some Consumer group. By adding more consumers to a Consumer group, you can balance the load. In general, the Consumer group reads data from the same topic. The number of partitions in a Topic always should be the same as Consumers in a particular CG (consumer group).

3. What is Fault-Tolerance?

Each partition is replicated on multiple servers. So, when one partition is failed, the other backup will deliver. So this concept is called Fault-tolerance.

4. Can we decrease the partitions that we created?

No, you can't decrease the partitions once created. But, you can increase the partitions.

5. What is the architecture of Kafka?

The architecture is a combination of Producer, Broker, Subscriber, and Zookeeper. It can handle messages from multiple producers. It can have multiple Brokers (Sometimes it is called Kafka Broker). Zoooker oversees the Kafka cluster and has information about consumer's messages.

6. How to start Kafka Broker?

In Linux environments, you can start using $ bin/kafka-server-start.sh config/server-1.properties

$ bin/kafka-server-start.sh config/server-2.properties

So, you start Kafka server using different Server properties. Here Server-1, Server-2, and so on.

7. What is Leader Balancing in Kafka?

A partition in a Broker acts as a leader. The partitions of replicas are followers of this leader. In case of failure, the followers act as leads and deliver messages to consumers. This is called Leader balancing.

8. What is the real use of Broker?

The Broker's main functionality is to handle the storage of messages in topics.

9. What are the two main functions of Zookeeper?

  • Oversee the function of the Kafka cluster (all the nodes)
  • It commits each offset after reading by the consumer. So, in case of Consumer failure, with the help of Zooker, the consumer starts reading from the next offset (after it recovered from failure)

 10. What is the Retention period?

The amount of Time that Kafka stores messages in Topics are called the retention period. There are two types of retentions - Time-based and Storage Based



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