The text provides an in-depth exploration of using KSQL, a continuous query language built on Kafka Streams, to detect fraudulent transactions in real-time by leveraging stream processing. It highlights the challenges faced in fraud detection across various industries, including banking and insurance, and explains how traditional methods often required advanced programming skills. The text introduces KSQL as an accessible solution that allows users familiar with SQL to build stream processing applications, enabling horizontal scalability and resilience. Through a detailed example involving ATM transactions, the text demonstrates how to use stream-stream joins and time windows to identify suspicious transactions. It describes the process of implementing a fraud detection system using Elasticsearch for data storage and Kibana for visualization, as well as integrating customer data from a MySQL database using Kafka Connect and Debezium to enrich the event stream with account details. The text concludes by emphasizing the scalability and flexibility of using KSQL and Kafka in developing real-time fraud detection systems and the potential for further action based on suspected fraud.