Hive : Understanding and Utilizing the ‘OFFSET’ Function in Apache Hive

Hive offers several powerful functions to users, enabling them to extract, manipulate, and analyze data stored in Hadoop clusters more efficiently. Among these functions, the ‘OFFSET’ function, while seemingly straightforward, is a highly useful tool that can drastically enhance the performance of certain types of queries.

What is OFFSET in Hive?

The ‘OFFSET’ keyword is used in the LIMIT clause to skip a number of rows in the result set before returning the queried data. Essentially, OFFSET allows users to define the starting point for the results returned by a SQL query. This is particularly useful when dealing with large datasets or when developing applications that need to display a certain subset of data.

When to Use OFFSET?

‘OFFSET’ is commonly used when implementing pagination in applications. In web applications that deal with large amounts of data, it’s impractical to load all data at once. Instead, data is loaded in chunks or pages. The ‘OFFSET’ function helps to handle this requirement efficiently by skipping the records that have already been fetched in previous pages.

For example, to fetch the second page of records while each page contains 10 records, you can set ‘LIMIT 10 OFFSET 10’. This command will skip the first 10 records and fetch the next 10.

Conversions Available

In Hive, the ‘OFFSET’ keyword is used along with the ‘LIMIT’ keyword in the SQL query. If your data source does not support the ‘OFFSET’ keyword, you may need to convert your query to use a ‘WHERE’ clause to achieve the same result. For example, if your original query was SELECT * FROM table LIMIT 10 OFFSET 20, you could convert this to SELECT * FROM table WHERE id > 20 LIMIT 10.

Example DDL + INSERT with OFFSET Use

Below is an example of a Hive table creation, data insertion, and a query using the ‘OFFSET’ function.

-- Create table
CREATE TABLE IF NOT EXISTS employees (
  id INT,
  name STRING,
  department STRING
);

-- Insert data
INSERT INTO TABLE employees (id, name, department)
VALUES 
(1, 'Sachin', 'Sales'),
(2, 'Ram', 'Marketing'),
(3, 'Lakshman', 'Sales'),
(4, 'Aishwarya', 'Marketing'),
(5, 'Kishore', 'Sales');

-- Query data using OFFSET
SELECT * FROM employees ORDER BY id LIMIT 2 OFFSET 2;