google-big-queryHow do I create and use a user-defined function (UDF) in Google BigQuery?

A user-defined function (UDF) is a type of function in Google BigQuery that allows you to write custom code in JavaScript to perform calculations on data stored in BigQuery.

To create a UDF, you must first define the function in JavaScript and then register it with BigQuery. Once registered, you can use the function in a SQL query.

For example, here is a UDF that takes a string and returns the string in uppercase:

CREATE TEMP FUNCTION to_uppercase(input STRING)
RETURNS STRING
LANGUAGE js AS """
  return input.toUpperCase();
""";

SELECT to_uppercase('hello world');

Output example

HELLO WORLD

The code consists of the following parts:

• CREATE TEMP FUNCTION: This statement registers the function with BigQuery.
• to_uppercase: The name of the UDF.
• input STRING: The parameter of the UDF.
• RETURNS STRING: The type of the return value.
• LANGUAGE js: The language used for the function.
• return input.toUpperCase();: The code that is executed when the UDF is called.
• SELECT to_uppercase('hello world');: This statement calls the UDF.

For more information on creating and using UDFs in BigQuery, see the BigQuery documentation.

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