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feat: add load balancing external functions
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‎docs/en/guides/54-query/03-udf.md

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---
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title: User-Defined Function
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---
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import IndexOverviewList from '@site/src/components/IndexOverviewList';
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import EEFeature from '@site/src/components/EEFeature';
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def remove_stop_words(text, stop_words):
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"""
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Removes common stop words from the text.
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Args:
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text (str): The input text.
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stop_words (set): A set of stop words to remove.
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Returns:
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str: Text with stop words removed.
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"""
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def calculate_sentiment(text, positive_words, negative_words):
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"""
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Calculates the sentiment score of the text.
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Args:
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text (str): The input text.
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positive_words (set): A set of positive words.
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negative_words (set): A set of negative words.
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Returns:
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int: Sentiment score.
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"""
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def get_sentiment_label(score):
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"""
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Determines the sentiment label based on the sentiment score.
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Args:
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score (int): The sentiment score.
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Returns:
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str: Sentiment label ('Positive', 'Negative', 'Neutral').
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"""
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def sentiment_analysis_handler(text):
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"""
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Analyzes the sentiment of the input text.
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Args:
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text (str): The input text.
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Returns:
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str: Sentiment analysis result including the score and label.
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"""
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clean_text = remove_stop_words(text, stop_words)
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sentiment_score = calculate_sentiment(clean_text, positive_words, negative_words)
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sentiment_label = get_sentiment_label(sentiment_score)
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return f'Sentiment Score: {sentiment_score}; Sentiment Label: {sentiment_label}'
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$$;
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```
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-- Insert sample data
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INSERT INTO texts (original_text)
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VALUES
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VALUES
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('The quick brown fox feels happy and joyful'),
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('A hard journey, but it was painful and sad'),
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('Uncertain outcomes leave everyone unsure and hesitant'),
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The following table shows the type mapping between Databend and JavaScript:
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| Databend Type | JS Type |
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|-------------------|------------|
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| ----------------- | ---------- |
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| NULL | null |
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| BOOLEAN | Boolean |
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| TINYINT | Number |
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## Managing UDFs
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Databend provides a variety of commands to manage UDFs. For details, see [User-Defined Function](/sql/sql-commands/ddl/udf/).
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Databend provides a variety of commands to manage UDFs. For details, see [User-Defined Function](/sql/sql-commands/ddl/udf/).

‎docs/en/guides/54-query/04-external-function.md

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---
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title: 'External Functions in Databend Cloud'
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sidebar_label: 'External Function'
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title: "External Functions in Databend Cloud"
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sidebar_label: "External Function"
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---
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External functions in Databend allow you to define custom operations for processing data using external servers written in programming languages like Python. These functions enable you to extend Databend's capabilities by integrating custom logic, leveraging external libraries, and handling complex processing tasks. Key features of external functions include:
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The following table lists the supported languages and the required libraries for creating external functions in Databend:
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| Language | Required Library |
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|----------|-------------------------------------------------------|
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| -------- | ----------------------------------------------------- |
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| Python | [databend-udf](https://pypi.org/project/databend-udf) |
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## Managing External Functions
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**Explanation of `@udf` Decorator Parameters:**
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| Parameter | Description |
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|--------------|------------------------------------------------------------------------------------------------------------------------------------------------------|
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| `input_types` | A list of strings specifying the input data types (e.g., `["INT", "VARCHAR"]`). |
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| `result_type` | A string specifying the return value type (e.g., `"INT"`). |
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| `name` | (Optional) Custom name for the function. If not provided, the original function name is used. |
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| `io_threads` | Number of I/O threads used per data chunk for I/O-bound functions. |
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| `skip_null` | If set to `True`, NULL values are not passed to the function, and the corresponding return value is set to NULL. Default is `False`. |
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| Parameter | Description |
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| ------------- | ------------------------------------------------------------------------------------------------------------------------------------ |
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| `input_types` | A list of strings specifying the input data types (e.g., `["INT", "VARCHAR"]`). |
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| `result_type` | A string specifying the return value type (e.g., `"INT"`). |
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| `name` | (Optional) Custom name for the function. If not provided, the original function name is used. |
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| `io_threads` | Number of I/O threads used per data chunk for I/O-bound functions. |
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| `skip_null` | If set to `True`, NULL values are not passed to the function, and the corresponding return value is set to NULL. Default is `False`. |
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**Data Type Mappings Between Databend and Python:**
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| Databend Type | Python Type |
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|-----------------------|----------------------|
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| BOOLEAN | `bool` |
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| TINYINT (UNSIGNED) | `int` |
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| SMALLINT (UNSIGNED) | `int` |
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| INT (UNSIGNED) | `int` |
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| BIGINT (UNSIGNED) | `int` |
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| FLOAT | `float` |
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| DOUBLE | `float` |
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| DECIMAL | `decimal.Decimal` |
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| DATE | `datetime.date` |
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| TIMESTAMP | `datetime.datetime` |
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| VARCHAR | `str` |
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| VARIANT | `any` |
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| MAP(K,V) | `dict` |
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| ARRAY(T) | `list[T]` |
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| TUPLE(T,...) | `tuple(T,...)` |
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| Databend Type | Python Type |
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| ------------------- | ------------------- |
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| BOOLEAN | `bool` |
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| TINYINT (UNSIGNED) | `int` |
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| SMALLINT (UNSIGNED) | `int` |
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| INT (UNSIGNED) | `int` |
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| BIGINT (UNSIGNED) | `int` |
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| FLOAT | `float` |
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| DOUBLE | `float` |
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| DECIMAL | `decimal.Decimal` |
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| DATE | `datetime.date` |
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| TIMESTAMP | `datetime.datetime` |
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| VARCHAR | `str` |
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| VARIANT | `any` |
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| MAP(K,V) | `dict` |
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| ARRAY(T) | `list[T]` |
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| TUPLE(T,...) | `tuple(T,...)` |
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### 3. Run the External Server
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SELECT gcd(48, 18); -- Returns 6
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```
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## Load Balancing External Functions
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When deploying multiple external function servers, you can implement load balancing based on function names. Databend includes a `X-DATABEND-FUNCTION` header in each UDF request, which contains the function name being called. This header can be used to route requests to different backend servers.
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### Using Nginx for Function-Based Routing
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Here's an example of how to configure Nginx to route different UDF requests to specific backend servers:
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```nginx
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# Define upstream servers for different UDF functions
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upstream udf_default {
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server 10.0.0.1:8080;
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server 10.0.0.2:8080 backup;
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}
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upstream udf_math_functions {
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server 10.0.1.1:8080;
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server 10.0.1.2:8080 backup;
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}
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upstream udf_string_functions {
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server 10.0.2.1:8080;
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server 10.0.2.2:8080 backup;
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}
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# Map function names to backend servers
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map $http_x_databend_function $udf_backend {
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default "udf_default";
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"gcd" "udf_math_functions";
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"lcm" "udf_math_functions";
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"string_reverse" "udf_string_functions";
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"string_concat" "udf_string_functions";
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}
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# Server configuration
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server {
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listen 443 ssl;
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server_name udf.example.com;
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# SSL configuration
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ssl_certificate /etc/nginx/ssl/udf.example.com.crt;
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ssl_certificate_key /etc/nginx/ssl/udf.example.com.key;
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# Security headers
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add_header Strict-Transport-Security "max-age=31536000" always;
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location / {
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proxy_pass http://$udf_backend;
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proxy_http_version 1.1;
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proxy_set_header Host $host;
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proxy_set_header X-Real-IP $remote_addr;
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proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
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proxy_set_header X-Forwarded-Proto $scheme;
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# Timeouts
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proxy_connect_timeout 60s;
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proxy_send_timeout 60s;
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proxy_read_timeout 60s;
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}
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}
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```
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When registering your functions in Databend, use the Nginx server's domain:
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```sql
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CREATE FUNCTION gcd (INT, INT)
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RETURNS INT
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LANGUAGE PYTHON
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HANDLER = 'gcd'
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ADDRESS = 'https://udf.example.com';
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```
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## Conclusion
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External functions in Databend Cloud provide a powerful way to extend the functionality of your data processing pipelines by integrating custom code written in languages like Python. By following the steps outlined above, you can create and use external functions to handle complex processing tasks, leverage external libraries, and implement advanced logic.

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