Flink SQL

Galaxy Glossary

What is Flink SQL, and how does it differ from standard SQL?

Flink SQL is an extension of standard SQL that allows you to query data streams in Apache Flink. It provides a familiar SQL syntax for processing data flowing through a stream processing engine.
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Description

Flink SQL is a powerful tool for working with streaming data. It leverages the capabilities of Apache Flink, a distributed stream processing framework, to enable SQL-like queries on data streams. Unlike traditional SQL, which operates on static datasets, Flink SQL processes data as it arrives, allowing for real-time analysis and transformations. This is crucial for applications like fraud detection, real-time analytics, and IoT data processing. Flink SQL provides a familiar SQL syntax, making it easier for developers already proficient in SQL to work with streaming data. It allows you to define complex transformations and aggregations on the data stream, enabling you to extract insights and perform actions in real-time.

Why Flink SQL is important

Flink SQL is important because it simplifies the process of working with streaming data. It allows developers to leverage their SQL knowledge to perform complex queries and transformations on data streams, enabling real-time insights and actions. This is critical for modern applications that require immediate responses to data changes.

Example Usage


-- Create a source that emits data every second
CREATE TABLE SensorReadings (
    sensor_id INT,
    temperature DOUBLE
) WITH (
    'connector' = 'connector:source', 
    'format' = 'json'
);

-- Define a sink to write the results to a file
CREATE TABLE OutputReadings (
    sensor_id INT,
    temperature DOUBLE
) WITH (
    'connector' = 'file', 
    'path' = '/tmp/output.txt'
);

-- Define a stream query to filter and aggregate data
INSERT INTO OutputReadings
SELECT sensor_id, temperature
FROM SensorReadings
WHERE temperature > 25
GROUP BY sensor_id
EMIT CHANGES;

Common Mistakes

Want to learn about other SQL terms?

With Cte In SQL

Common Table Expressions (CTEs) are temporary, named result sets defined within a single SQL statement. They enhance query readability and reusability by breaking down complex queries into smaller, manageable parts.

Where Vs Having SQL

WHERE and HAVING are both used for filtering data in SQL, but they operate on different levels. WHERE filters rows before any aggregation, while HAVING filters groups after aggregation.

Windows Functions In SQL

Window functions in SQL perform calculations over a set of rows related to the current row, unlike aggregate functions which summarize data across all rows. They are powerful tools for analyzing data within a specific context.
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