What are user-defined functions (UDFs) in BigQuery?
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User-Defined Functions (UDFs) in BigQuery
custom functions that allow you to extend SQL's capabilities by writing your own logic using SQL or JavaScript. UDFs are useful when built-in SQL functions are not sufficient for the data transformation or computation you need.
🔹 Types of UDFs in BigQuery:
SQL UDFs
These are written using standard SQL expressions and can reuse logic across multiple queries.
Example:
sql
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Edit
CREATE FUNCTION my_dataset.add_numbers(a INT64, b INT64)
RETURNS INT64 AS (
a + b
);
JavaScript UDFs
These allow more complex logic using JavaScript.
Example:
sql
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CREATE TEMP FUNCTION toUpperCase(str STRING)
RETURNS STRING
LANGUAGE js AS """
return str.toUpperCase()
🔹 Use Cases for UDFs:
Complex data transformation not supported by standard SQL
Reusable business logic (e.g., currency conversion, string formatting)
Text processing using JavaScript (e.g., regex, NLP)
🔹 Key Features:
Modular & Reusable: Define once, use in multiple queries.
Secure: Executed in a sandboxed environment.
Temporary or Persistent: Can be created for a session or stored in a dataset.
🔹 Best Practices:
Use SQL UDFs where possible for better performance.
Avoid heavy logic in JavaScript UDFs for large datasets.
Document and version persistent UDFs in shared datasets.
In summary, UDFs in BigQuery offer flexibility to perform custom operations on your data, making them a powerful tool for advanced data processing tasks.
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